DRUGS AND MEDICINES MODULE - 8 OBJECTIVES. Notes

Transcription

1 Drugs ad Medicies MDULE DRUGS AND MEDICINES The associatio of makid with pai ad disease is probably as old as ma himself. Humas have always bee lookig for remedies to overcome their pai ad sufferig. The earliest attempts at this, ivolved use of various plats. The kowledge was based o experiece ad was haded o from geeratio to geeratio. It is beig used eve today. I a attempt to coquer pai ad disease, a large umber of sythetic chemicals have bee discovered. The chemicals used as medicies are kow as pharmaceuticals. Today pharmaceutical idustry has grow to be oe of the biggest idustries i the world. I this lesso we will try to itroduce you to the area of drugs ad medicies. I the process we would attempt to differetiate betwee drugs ad medicies (though commoly used iterchageably). You will also lear about classificatio of medicies ad other importat aspects of drugs ad medicies. BJECTIVES After readig this lesso you will be able to : defie drugs ad medicies; differetiate betwee drugs ad medicies; classify medicies o the basis of their actio (use); cite examples ad effects of aalgesics, atipyretic, atiseptics, disifectats, atacids, atimalarials, aaesthetics, atimicrobials (sulpha drugs ad atibiotics), ati-fertility drugs, etc.; differetiate betwee aalgesics ad atipyretics; differetiate betwee atiseptics ad disifectats; 387

2 MDULE - 8 Drugs ad Medicies explai habit formig ad o-habit formig drugs; differetiate betwee broad spectrum ad arrow spectrum atibiotic; differetiate betwee local ad geeral aaesthetics; describe self-medicatio ad alterate systems of medicie WHAT ARE DRUGS AND MEDICINES? Whe we fall ill we take some tablets, pills, ijectios or apply some oitmets to get well. All these are collectively kow as medicies. Some time we may use some parts of plats or some preparatios made from herbs, mierals, aimals, etc. All these substaces used for the treatmet or prevetio of diseases, ca also be called medicies. Medicies cotai a sigle chemical or a umber of chemicals i differet amouts to have the desired effect. The mode of actio of the chemicals of a medicie is quite varied ad complicated. I may a cases mode of actio may ot be fully kow to us, but we cotiue to use them as they are useful to us. Early ma used several plats or parts of plats to cure diseases, without kowig of the chemical compoets, resposible for it. For example bark of willow tree was used for relievig pai (as aalgesic). Later, it was foud that its bark cotaied 2-hydroxy bezoic acid, which is closely related to acetyl salicylic acid (also kow as aspiri). Parts of a plat Rauwolfia serpetia (Hidi ame, sarpagadha) have bee used i Ayurvedic drugs for the treatmet of hypertesio (high blood pressure). Later o it was discovered that a compoud called reserpie was resposible for reducig blood pressure. Thus reserpie became the first moder medicie to cotrol blood pressure. I most of the cases ature led to the discovery of moder medicie. Thousads of chemists all over the world are costatly searchig for better, efficiet, cheaper ad safer medicies. As metioed earlier the term drugs ad medicies are used iterchageably, but there is a differece betwee the two. Let us try to uderstad the differece betwee drugs ad medicies. The term drug is ofte used for preparatios or formulatio whose chemical compoets ad their quatities are ot kow fully. These may be extracts of certai plats, herbs, aimal parts or may be mierals. The term medicie is used whe the chemical compositio ad the quatities of various chemical compoets are kow. Further, the effects of the chemical compouds preset i a medicie ad their side effects have bee properly ad extesively studied. The medicies are approved by the relevat govermetal authorities like Drug Cotroller of Idia. 388

3 Drugs ad Medicies The term drug is also used for substaces, which are habit formig ad are ofte abused, for example, arcotics like cocaie, morphie, heroie, marijuaa, etc. MDULE - 8 As you read i ewspapers terms like illegal drug trade, drug traffickig, drug mafia, drug peddler are used to refer to illegal dealig with habit formig substaces, referred to as drugs. However the differece betwee drug ad medicie is far from clear. INTEXT QUESTINS Write a defiitio of medicies. 2. Most of the chemicals used i medicies are poisoous. Is this statemet true or false? 3. What are pharmaceuticals? 4. Name the compoud which is preset i the plat sarpagadha ad is resposible for reducig blood pressure CLASSIFICATIN F MEDICINES You may be familiar with some of the commo medicies used for relievig pai, reducig fever or for treatig commo cold, etc. The umber of medicies is very large therefore medicies are classified accordig to their actio or use. Table 30.1 provides a list of some importat classes of medicies. The terms like aalgesics, atibiotics, atiseptics, etc. are commo household words. Let us try to uderstad the meaig of this classificatio i a little more detail. Table 30.1 : Some Importat Classes of Medicies ad their Actio S.No. Class Actio or Usage 1. Atipyretics Reduce body temperature 2. Ati histamies Reduce allergy 3. Aalgesics Reduce pai 4. Atimalarials Used for treatmet of malaria 5. Germicides Kill germs 6. Atiseptics Kill germs (ca be safely used o livig tissue) 7. Disifectat Kill germs (caot be used o livig tissue) 8. Atacids Reduce acidity i stomach 9. Aaesthetics Loss of sesatio 10. Atimicrobials, Kill microorgaisms Sulpha drugs ad Atibiotics 11. Traquilizers ad hypotics Reduce axiety ad brig calmess 12. Birth Cotrol Medicies Birth cotrol (Cotraceptives) 389

4 MDULE Atipyretics Drugs ad Medicies Atipyretics are the substaces which are used to reduce body temperature or to cotrol fever. The word atipyretic is derived from pyro which meas fire (meas hot) ati meas agaist. Thus atipyretic meas it couteracts heat (high body temperature). Aspiri, paracetamol ad pheaceti are commoly used atipyretics. You get them i the market with differet trade ames like croci, aaci, dispri, etc. H C 2 H 5 CH 3 CH NH-CCH 3 NH-CCH 3 Aspiri Paracetamol Pheaceti Aspiri is the most popular atipyretic i use. It gets hydrolyzed i stomach ad salicylic acid is released. verdose ad usig it over a log time may cause side effects. It may cause bleedig i the stomach wall ad eve ulcers. Therefore, overdose ad prologed use should be avoided. However, calcium ad sodium salts of aspiri are more soluble i water ad are less harmful tha aspiri. 2. Aalgesics Aalgesics are the substaces, that reduce pai which may be due to swellig of tissues, ijury, iflammatio or some other disorders. Aalgesics are of two types, amely arcotic & o-arcotic. Narcotic aalgesics are the oes which iduce sleep ad thus help to reduce the feelig of pai alkaloids preset i opium, viz. morphie, codeie, etc. are commo examples of arcotics. I higher doses these may cause ucosciousess. These are habit-formig ad cause addictio. Due to addictio a perso wats to have it regularly ad i larger amouts. Such a perso feels upset ad ucomfortable if he doesot get it. Narcotic aalygesies do ot iduce sleep ad are ot habit formig. A commo example of this type of arcotics is morphie. H 3 C N H H H Morphie 390

5 Drugs ad Medicies 3. Atimalarials Atimalarial medicies are used to treat malaria. Quiie ad chloroquie are widely used atimalarials. Quiie is oe of the earliest drugs, which was first obtaied from the bark of a plat (cichoa) ad later o sythesized i laboratories. CH 2 MDULE - 8 CH 3 H H C N N Quiie 4. Atihistamies Some persos are hypersesitive towards some medicies like peicilli, sulpha drugs ad may be sesitive to food ad eviromet due to differet sesitizig substaces (atiges) derived from them. The hypersesitivity is called allergy. It is due to release of a chemical substace called histamie i the body. Athistamie are the chemical substaces (drugs) which cotrol or abolish the effect of histamies released i the body. These drugs are also called atiallergic drugs. Histamie is also resposible for the asal cogestio (discharge), mild asthama associated with commo cold, cough, allergic respose to pollegrais etc. Histamie cotract the smooth muscles i brochi ad gut, relaxes other muscles preset i the walls of fie blood versels. Atihistamie are widely used for treatmet of hay-fever, itchig of eyes, ose ad throat, cojuctivities. Some atihistamie drugs are diphehydramie (Beadryl) pheiramie maleate (Avil) chlorspheiramie maleate (zect), citrazie ad terfeadie (seldae) Ph N H Ph H Seldae 391

6 MDULE Germicides, Disifectat ad Atiseptic Drugs ad Medicies Germicides are the chemicals, which prevet growth of germs (microorgaisms). Germicides are classified as atiseptic ad disifectat. Both kill microorgaisms but the differece lies i the way we use them. Atiseptics kill microorgaisms ad are safe to be used o livig beigs (tissues). Atiseptics are used o wouds, cuts or ski abrasios. These are used to dress wouds, etc. For example, iodoform (CHI 3 ), ticture of iodie, ethyl alcohol, a 0.2 percet aqueous solutio of pheol ad boric acid (H 3 B 3 ) are commo atiseptics. Some dyes have the ability to kill microorgaisms. These dyes were the earliest compouds to be used as atiseptics. Examples are acriflavie (a yellow coloured dye), mercurochrome (a red coloured dye), methylee blue (a blue coloured dye). These dyes are still i use as atiseptics. Iodie is a powerful atiseptic. It is used as ticture of iodie. Ticture of iodie is 2 to 3 percet solutio of iodie dissolved i ethyl alcohol. Iodoform is a yellow coloured solid, which is used as a atiseptic. Disifectats kill germs (microorgaisms) but are used o o-livig substaces like surgical istrumets, floors, bathrooms, lavatories, etc. Disifectats are harsh ad are ot safe to be used o livig beigs as disifectats ca damage livig tissues. Chlorie is a powerful oxidizig aget. It is used for disifectig water. A cocetratio of 0.2 to 0.4 ppm (parts per millio) is eough to kill microorgaisms preset i water. Low cocetratio of sulphur dioxide is used to kill microorgaisms i jams, jellies ad squashes. Thus it acts as a food preservative. Sulphur dioxide is used for fumigatio i rooms, operatio theaters, etc. to sterilize them. Bleachig powder (CaCl 2 ), chlorie (Cl 2 ), mercuric chloride (HgCl 2 ), sodium hypochlorite (NaCl), sulphur dioxide (S 2 ) etc. are other examples of disifectats. Is Pheol Atiseptic or Disifectat? It is iterestig to ote that 0.2 percet aqueous solutio of pheol is used as atiseptic by makig. It is safe to be used o livig tissues i low cocetratios (less tha 0.2 percet). If cocetratio of pheol is high the it ca damage tissues. Therefore, at higher cocetratio (1 percet or more) pheol is used as disifectat. 392

7 Drugs ad Medicies H Cl H MDULE - 8 H 3 C H Pheol Chloro-xyleol H H H CH 3 CH 3 CH 3 o-cresol m-cresol p-cresol Most atiseptics ad disifectaits are powerful poisos (Table 30.2). They are able to kill microorgaisms as they iterfere with their metabolism. While some others are able to kill microorgaisms because of their powerful oxidizig or reducig ature (Table 30.2). Table 30.2 : Nature of Some Importat Atiseptics ad Disifectats Poisos xidisig agets Reducig agets Dyes Acriflavie (a yellow dye) Bleachig powder Sulphur dioxide Getia violet Chlorie Mercurochrome Hydroge peroxide Methylee blue Iodie Ticture of iodie Pheols Pheol Cresols Resorciol Chloroxyleol Iodoform Potassium permagaate Sodium hypochlorite thers Formaldehyde Boric acid Mercuric chloride Silver itrate 393

8 MDULE Atacids Drugs ad Medicies Atacids are the medicies which eutralize the excess acid preset i the stomach. Stomach juice cotais hydrochloric acid (HCl). This acid helps the process of digestio of food. Due to illess or axiety or some other reasos more acid is produced i the stomach. The stomach juice becomes more acidic tha ecessary. This causes problems i digestio, bleedig i the liig of stomach or eve ulcers. Some medicies are used to eutrialise the excess acid ad correct the ph of the stomach fluid. For example, sodium bicarboate (NaHC 3 ) or a suspesio of magesium hydroxide is used to eutralize excess of acid preset i the stomach. Milk of magesia cotais magesium hydroxide, EN fruit salt cotais sodium bicarboate which helps to eutralise excess acidity i the stomach juice. Medicie like digee, gelusil, used as a atacid cotai magesium hydroxide. 7. Atimicrobials May diseases are caused due to ifectio i the body by certai microorgaisms (bacteria, fugus or viruses). Some examples of diseases caused by microbes are dysetry, peumoia, typhoid, uriary tract ifectio, etc. Atimicrobials are the chemicals, which are used to kill microorgaisms (which has ifected the body) without causig much damage to the body of the patiet. Thus a atimicrobial is a chemical, which is capable of curig diseases caused by various microbes. A ideal atimicrobial should kill disease-causig microbe ad should ot have ay harmful effect o the patiet. I fact there may ot be ay such atimicrobial which is totally safe ad without ay side effect. The most commo atimicrobials available are the sulhpa drugs ad atibiotics. 8. Atibiotics Atibiotics are the metabolic products produced by some microorgaisms (mould or fugi). They ihibit growth ad eve kill disease causig microorgaisms (like bacteria, fugi, etc) by ihibitig their life processes. Therefore they are referred to as atibiotics (ati meas agaist ad biotic meas life). Peicilli was the first atibiotic to be discovered. Alexader Flemig isolated peicilli i 1929 from a mould Pecillium otatum. Peicilli has bee used for the treatig diseases caused by several bacteria. It has bee effectively used for treatmet of peumoia, brochitis, sore throat, abscesses, etc. 394

9 Drugs ad Medicies Later o attempts have bee made to improve the quality of peicilli. It has led to the discovery of differet varieties of peicilli. For example, Peicilli G (also kow as bezyl peicilli), peicilli F, peicilli K are the more commo varieties of peicilli. MDULE - 8 H N S CH 3 N CH 3 CH Peicilli G (bezyl peiclli) Ampicilli ad amoxicilli are the semi-sythetic modificatios of peicilli. I this case the metabolic product of mould is obtaied ad the some reactios are carried out to brig the desired chages i the atibiotic molecule to get ampicilli or amoxicilli. Attempts are beig made to discover better ad better atibiotics. This search for fidig better atibiotics is a ever-edig process. Now a large umber of atibiotics are available. Some examples are streptomyci ad chloromyceti (chloroampheicol) ad tetracyclie. 2 N H CH CH 2 H Chloroampheicol H N C CHCl2 Streptomyci is used for the treatmet of tuberculosis (TB). Chloromyceti is used for the treatmet of typhoid. Tetracyclie is used for the treatmet of several diseases. Broad-spectrum atibiotics are those atibiotics, which kill a wide rage of diseasecausig microorgaisms. Broad-spectrum atibiotics ca be used for the treatmet of several diseases. For example, streptomyci, tetracyclie ad chloroampheicol are broad-spectrum atibiotics. Narrow spectrum atibiotics are effective i the treatmet of a few diseases. 9. Allergic Reactios of Atibiotics Some people may show allergic reactios to some atibiotics. These reactios may be mild like rashes appearig o the ski or may be very serious ad ca 395

10 MDULE - 8 Drugs ad Medicies eve be fatal. You might have observed that a doctor gives a small dose of atibiotic by ijectio ad the waits for some time to watch if there is ay uwated reactio. If there is o adverse (bad) reactio, the oly the doctor gives the full dose of the atibiotic. 10. Traquilizers ad Hypotics Traquilizers ad hypotics are used to reduce axiety, ad they also make a perso calm. Sleepig pills are made up of these compouds. Most of them are habit-formig. Their idiscrimiate ad over use should be avoided. therwise it may lead to addictio ad may other complicatios, CH 3 H 5 C 2 H 7 C 3 Ph NH NH N H N H Lumial Secoal Lumial, secoal ad equail are the most commoly used traquilizers. Barbituric acid ad some other compouds related to barbituric acid are used i makig sleepig pills. NH CH 3 N H H 2 N NH 2 CH 3 Barbituric acid Equail 11. Fertility Cotrol Medicies It is a cocer of everyoe to cotrol huma populatio. Medicies are available which help prevet pregacy. The medicies, which help prevet pregacy, are kow as cotraceptives. These are geerally available i the form of tablets ad are to be take regularly by females. Chemicals like orethidroe ad mestraol are used as cotraceptives (birth cotrol pills). Chemically these are similar to female sex hormoes. 396

11 Drugs ad Medicies MDULE - 8 CH H CH 3 CH H Norethidroe Me Mestraol The birth cotrol pills may have some side effects i some cases. Therefore, the birth cotrol pills should be used uder the guidace of some expert HAZARDS F SELF MEDICATIN Whe medicies are take by a patiet without the advice of a qualified doctor, it is called self-mediatio. Self-medicatio is very harmful ad a dagerous practice. e should ever try self-medicatio. Some of the harmful effects are: 1. A medicie, which has worked well for some oe, may ot be good for you ad ca eve cause some serious harm. 2. You may take a medicie i quatity more tha ecessary. It may be harmful for you. 3. You may take quatity less tha ecessary. The disease-causig microorgaisms may gai resistace to the medicie ad the medicie may become ieffective. You should avoid self-medicatio. Without advice of a doctor avoid use of commo medicies over prolog periods. Improper use of eve most commo medicies, which are readily available without a prescriptio of a doctor, ca have harmful effect. The medicies, which you ca buy without a prescriptio of a doctor, are called over-the-couter medicies. For example cough syrups, croci, aspiri, etc are over the couter medicies. The medicies, which you ca buy after showig a prescriptio of a qualified doctor, are kow as scheduled drugs. Improper use of scheduled drugs is likely to cause more serious problems. Therefore, their sale is cotrolled ad regulated by the govermet. Most of good chemists do ot sell scheduled medicies without a proper prescriptio. Some irresposible chemists may sell such medicies without a prescriptio. It is ot a good practice you should ot ecourage it. 397

12 MDULE - 8 Drugs ad Medicies INTEXT QUESTINS Give two examples of atipyretics. 2. Give oe example of a arcotic type aalgesic. 3. What is the differece betwee a atiseptic ad disifectat? 4. What are atacids? Name two chemicals commoly used as atacids. 5. What is the differece betwee local aaesthetic ad geeral aaesthetic. 6. Defie atibiotics. Give oe example of a atibiotic. 7. Which type of medicies are usd i hey-fever, itchig of eyes; ose ad throuts. 8. What is the use of traquilizers ad hypotics? 9. Give oe example of a traquilizer. 10. What are cotraceptives? 11. What are over the couter medicies? Chemicals i foods Preservatives ad artificial sweeteig agets Food Preservatives: Chemical substaces which are used to protect food materials agaist microorgaisms (bacteria yeasts ad moulds) are called preservatives. Some commoly used preservatives are 1. Commo Salt, Sugar ad oils: The sufficiet amout of salt resist the activity of microorgaisms i food it is called saltig. It is used to preserve raw mago, bea, fish ad meat, etc. Sugar syrup used for preservig like apple, mago, amla ad carrot etc. Sugar, oil, viegar & citric acid are used to preserve pickles, ketchups ad jams, etc. 2. Sodium bezoate (C 6 H 5 CNa): It is used for preservig of food material like fruit juices, soft driks, squashes ad jams. It is soluble i water. It is metabolized as hippuric ad which is excreted i urie. 3. Sodium meta bisulphite (Na 2 S 2 5 ): Its preservative actio is due to S 2 which from sulphurous acid whe dissolved i water. It also ihibits the growth of yeasts, moulds ad bacteria. It is used to preserve fruitams, juices, squashes, pickles, apples, etc. 4. Sodium ad Potassium Salts of propioic acid, sorbic acid are also used as preservatives. 398

13 Drugs ad Medicies Atioxidats The usaturated fat ad oils are readily oxidized o storage, the taste ad smell are chaged ad become racid. To prevet this oxidatio, racidity ad spoilage, certai chemical substaces are added, are called atioxidat (food additives). Whe these are added to food items cotaiig fats ad oils retard the oxidatio because they are more reactive towards oxidatio tha fats ad oils. So the oxidatio of food is preveted. Atioxidats react with free radicals ad stop the oxidatio of food. The most familiar atioxidats are butylated hydroxyl toluee (BHT) ad butylated hydroxyl aisole (BHA) C(CH ) 33 C H C(CH ) 33 (CH ) 3 C H C(CH ) 33 MDULE - 8 CH 3 CH 3 (BHA) (BHT) These are added to butter, meats, cereals chewig gum, sack gum, baked food ad beer etc. It icreases the life of food from moths to years. It shows more active syergetic effect whe added with Vitami C (ascorbic acid) ad citric acid Artificial Sweeteig Agets The chemical compouds which give sweeteig effect to the food are called sweetig aget. Sucrose ad Glucose are widely used as atural sweeteig aget. The excess itake of atural sugar cause to obesity diabetics ad tooth decay. Natural sugar is a good source of eergy. While the artificial sweeteig agets does ot provide eergy. It is excreted from the body i urie uchaged. Some commoly used artificial sweeteig agets are sacchari, aspartame, alitame, sucrolose, etc. 1. Sacchari (-Sulpho bezimide) Sacchari is isoluble i water but sodium salt is highly soluble i water. It is 550 times sweeter tha sugar. It is ot metabolized by our body. So it does ot provide eergy ad has o calorific values. C NH C + N Na S 2 Saccharie (Isoluble iwater) S 2 Sodium salt of Saccharie (Solube i water) 399

14 MDULE - 8 Drugs ad Medicies 2. Aspartame It is methyl ester of dipetide derivative derived from aspartic acid ad pheylalaie. It is 100 times as sweet as sugar. It is ustable at cookig temperatures. It is used i cold driks ad soft driks. It is a exceptio because the body breakes it dow i to amio acid ad methol. H CCH CH C NH CH C CH 2 3 NH 2 CH 2 (Aspartame) 3. Alitame: It is very high potecy sweeteer, It is about 2000 times sweeter tha sugar. It is more stable at cookig temperatures. It is very difficult to cotrol the sweetess of food. 4. Sucrolose: It is trichloro derivative of sucrose. It s taste is like sugar. It is also stable at cookig temperatures. It is about 600 times sweeter tha sugar. Sucrolose is expected to become a great commercial artificial sweetig aget. INTEXT QUESTINS What type of chage take place o storage the fat & oil? 2. Write the ame of preservative used with soft driks. 3. What chage will take ier body o takig exercise sugar (N). WHAT YU HAVE LEARNT Medicies are the chemicals or mixture of chemicals used for the prevetio, cure, treatmet, maagemet of diseases ad disorders or recovery of patiets Medicies are obtaied from plats or parts of plats or sythesized i laboratories. Medicies may cotai oly oe chemical compoud or it may be a mixture of several compouds. Drugs may be the crude mixtures ad the idetity of all the chemical compoets ad their amout preset i them may ot be accurately kow. Atipyretics are used to reduce body temperature for example aspiri ad paracetamol. 400

15 Drugs ad Medicies Aalgesics reduce body pai for example aspiri ad morphie. Atiseptics kill microorgaisms ad are safe to be used o a livig tissue while disifectats are used o iaimate objects. Aqueous solutio (less tha 0.2 percet) of pheol is used as a atiseptic. I higher cocetratios pheol is used as a disifectat. Atibiotics are the metabolic products produced by certai microorgaisms which ca kill some microorgaisms. For example peicilli, streptomyci, tetracyclie, etc. Broad spectrum atibiotics ca kill several differet microorgaisms, therefore, ca cure several diseases. storage the taste ad smell are chaged ad become racid. Certai chemical substaces are added to cotrol oxidatio spoilage ad racidity. Butylated hydroxyl toluee (BHT) ad Butylated hydroxyl aisole (BHA). Commo Salt, sugar ad oils are atural food preservatives. Sodium bezrate is familiar food predervative. Aspartame is ustable at cookig temp. so used i cold driks ad soft driks. Alitame is more stable at cookig temp. Suerolose is mare stable at coolig tamp ad easy to cotrol the sweetess of food. MDULE - 8 TERMINAL EXERCISE 1. How are medicies classified? 2. Who isolated the first atibiotic? 3. Name a medicie, which is used as aalgesic as well as atipyretic. 4. What is a o-arcotic aalgesic? 5. Why is 2.0 percet aqueous solutio of pheol used as a disifectat? 6. What do you uderstad by allergic reactios of atibiotics? 7. What are scheduled drugs? 8. Which medicies ca you purchase without the prescriptio from a doctor? 9. What is self-medicatio? Describe some of its ill effects. 10. Write the two ames of chemicals which icreases the life of food from moths to years. 11. Which artificial sweateig agets is more suitable at cookig temperatures. 12. Which is resposible for perservatio actio of sodium meta bisulphite? 401

16 MDULE ANSWERS T INTEXT QUESTINS Drugs ad Medicies 1. Medicies are all those substaces or formulatios which are used for cure, treatmet, prevetio of diseases or disorders ad recovery of a patiet. 2. True 3. Pharmaceuticals are the chemicals which are used as medicies. 4. Reserpie Aspiri ad Paracetamol. 2. Morphie. 3. Disifectats kill germs but ca damage livig tissues Aticeptics are safe for livig tissues ad yet kill germs. 4. Medicies used to eutralise excess acid i the stomach. Magesium hydroxides ad sodium carboate. 5. Local aesthetics cause loss of sesatio of pai over a small area while geeral aesthetics cause loss of cocsiousess. 6. Metabolic products of certai microorgaisms ad ca kill some other microorgaisms. Peicili is a example of atibiotic. 7. Ati histomies are used. 8. Traquilizers ad hypotics are used to reduce axiety ad these also make a perso calm. 9. lumial 10. Cotraceptives are the medicies used for prevetio of pregacy. 11. ver-the-couter medicies are those which ca be purchased without a prescriptio from a doctor storage of fat ad oil get oxidised, the taste ad smell are chaged ad become racid. 2. Sodium bezoate (C 6 H 5 CNa) is used as perservative with soft driks. 3. The excess itake of atural sugar cause to obesity ad tooth decay. 402

17 Soap, Detergets ad Polymers MDULE SAP, DETERGENTS AND PLYMERS I the previous lesso module VII you have studied about the chemistry of orgaic compouds. I this module you would lear about the meaig of soaps, detergets ad polymers. The sythetic detergets are better tha soaps but due to o biodegradibility causes water pollutio ad soil pollutio. You would also lear about type of soaps ad detergets. Today polymers have iflueced our life style to the extet that it would ot be wrog to say that we are i polymer age. Nowa-days polymers fid wide rage of uses startig from commo household utesils, automobiles, clothes, furiture, etc., to space-aircraft ad biomedical ad surgical compoets. Polymeric materials are light weight but ca possess excellet mechaical properties ad ca be easily processed by differet methods. I this lesso you would lear more about polymers, their types ad some importat-sythetic ad atural polymers. BJECTIVES After readig this lesso, you will be able to : distiguish betwee soaps ad detergets; explai types of detergets; list advatages ad disadvatages of detergets over soaps; explai cleasig actio of soaps ad detergets; defie the terms like moomers, polymer, homopolymer, copolymer ad polymerizatio; classify polymers o the basis of their source, molecular forces ad method of preparatio; 403

18 MDULE - 8 Soap, Detergets ad Polymers list the moomers of the polymers like atural ad sythetic rubber; list the moomer of the polymer like polythee, polystyree, Bua- S, PMMA, PVC, teflo, polyester, Nylo 66 ad Nylo 6; defie biodegradable polymers; ad cite examples of some biopolymers CLEANSING AGENTS (SAPS AND DETERGENTS) Soaps ad detergets are widely used as cleaig agets. Chemically soaps ad detergets are quite differet from each other. The commo feature of soaps ad detergets is that whe dissolved i water the molecules of soap ad deterget ted to cocetrate at the surface of the solutio or at iterface. Therefore, the surface tesio of the solutio is reduced, it causes foamig of the solutio. Soaps ad detergets lower the surface tesio of the solutio. Such substaces are called surface-active agets or surfactats. To sum up, soaps ad detergets: 1. are used as cleasig agets 2. cause foamig of the solutio 3. lower surface tesio 4. molecules ted to cocetrate ear the surface of the solutio 5. are the surface active agets 6. are the surfactats 7. ca emulsify grease 8. ca remove dirt, etc. Hydrophilic ad Lipophilic Parts Both soap ad deterget molecules have two parts. e part of the molecule is polar (ioic) i ature. Polar ature is due to the presece of groups like carboxylate ( C ) or sulphoate ( S 3 ). The polar group is a hydrophilic group. The hydrophilic group makes soaps ad detergets soluble i water. The other part of the soap or deterget molecule is o polar (oioic) that is lipophilic. The lipophilic part (a log chai alkyl or a log chai substituted aryl group) makes the molecule oil soluble. Depedig o the ature of the hydrophilic (polar) part i the soap or deterget molecule these are classified as aioic, catioic or o-ioic type. For example, soap has a carboxylate aio therefore soap is aioic type (table 8.5.1). Sythetic detergets have sulphoate aio thus they are also classified as aioic type. Aioic types are the most commo. However, catioic ad o-ioic detergets are also kow. 404

19 Soap, Detergets ad Polymers Soaps Soaps are the sodium or potassium salts of log chai fatty acids. These fatty acids are preset i oils ad fats i the form of glycerides. The glycerides preset i oils ad fats are the esters of glycerol ad log chai carboxylic acids for example palmitic acid ad stearic acid. Sapoificatio Sapoificatio is the process of makig soap. Sapoificatio is doe by hydrolysis of oils or fats (of vegetable or aimal origi) with the help of alkali like sodium hydroxide (NaH) or potassium hydroxide (KH) MDULE - 8 CH 2 CR CH CR CH 2 CR il or fat CH 2 H + 3NaH CH H + 3 RCNa CH 2 H Soap glycerol (where R= log chai alkyl group cotaiig 11 to 17 carbo atoms) Sythetic Detergets Sythetic detergets are used as cleaig agets much like soaps. Chemically, detergets are sodium salts of log-chai alkyl hydroge sulphate or sodium salts of log-chai alkyl bezee sulphoic acids. (Remember that soap is a sodium or potassium salt of log-chai fatty acid.) C R Na + R S Na+ (Soap) (Deterget) Deterget molecules are similar to that of soap molecules, that is they have a oil-soluble (lipophilic) log chai of carbo atoms ad a polar (hydrophilic) watersoluble part. For example, sodium lauryl sulphate (C 12 H 25 S 3 Na) has a 12 carbo atom hydrocarbo like alkyl chai. The log carbo chai is oil-soluble (lipohilic) part ad the sulphate is polar (hydrophilic) part that makes the molecule water-soluble. The water-soluble part is referred to as water-soluble head ad the log chai of carbo atoms is referred to as oil-soluble tail. S Na + o polar part il soluble (tail) polar part water soluble (head) 405

20 MDULE Cleasig actio of soap ad detergets Soap, Detergets ad Polymers The molecules of soaps ad detergets are smaller tha the colloidal particles. These molecules associate ad get the colloidal particle size rage. This associate form is kow as micelles. Soap ad detergets dissociate i ios whe dissolve i water beig electrolyte i ature. C 17 H 35 CNa C 17 H35C + Na + Soap The log chai of hydrocarbo, which is hydrophobic is ature (isoluble i water) directed towards the cetre while the head (hydrophylic water soluble part) is o the surface i cotrol of water. The iitial cocetratio at which micellizatio begis is called critical micellizatio cocetratio (CMC). The formatio of micelles starts above a defiite temp, that is called kraft temperature (TK). The cleasig actio of soap is due to micelles. The micelles are absorbed by grease/dirt i cloth. Because both are o polar. The polar head is directed towards water the rubbig by hads or mechaical stirrig break the grease particles i to smaller droplets ad form emulsio with water. As a result, the cloth gets free from dirt ad grease. The droplets ad washed away with water Advatages ad Disadvatages of Sythetic Detergets The sythetic detergets are better tha soaps i certai respects. Sythetic detergets ca be used for washig of clothes eve if the water is hard. Calcium ad magesium ios preset i hard water make correspodig salts with deterget molecules. The calcium ad magesium salts of deterget molecules are soluble i water (ulike that formed by soap molecules). However, deterget cotaiig brached alkyl bezee sulphoate is ot completely biodegradable (Table 32.2). Soap is completely biodegradable. Therefore, excessive use of sythetic detergets is a cause of worry. The problem 406

21 Soap, Detergets ad Polymers has bee partly solved by usig liear alkyl bezee sulphoate, which has better bio-degradability the the brached alkyl bezee sulphoate (Table 31.1) MDULE - 8 Table 31.1 : Bio-degradability ad class of soaps ad some sythetic detergets Deterget Class Polar Group Bio-degradable Soaps aioic Carboxylate 100% Brached alkyl aioic Sulphoate 50-60% bezee sulphoate Liear alkyl aioic sulphoate 90% bezee sulphoate Lauryl alcohol aioic Sulphate 100% INTEXT QUESTINS What is the active compoet i soaps? 2. What are the raw materials used for the maufacture of soaps? 3. What is the polar part i a soap molecule? 4. What is the polar part (hydrophilic) i a sythetic deterget molecule? 5. What is the oil-soluble (lipophilic) part i the soap molecule? 6. Brached alkyl bezee sulphoate is more bio-degradable tha liear alkyl bezee sulphoate. Is it true or false? 31.2 WHAT ARE PLYMERS A Polymer is a giat molecule formed by iter molecular likage betwee same or differet types of smaller molecules called moomers. If a large umber of moomers (A) are liked together the the polymer is represeted as ( A ) ( A A A A A) is a polymer of the moomer of (A). For example, polyethee ( CH 2 CH 2 ) is a polymer of the moomer ethylee (CH 2 = CH 2 ). Polymer is a high molecular mass molecule formed by likig up of two or more small molecules called moomers. Moomers are the small molecule which are capable of likig amogst themselves to form big molecules called polymers. I some polymers more tha oe type of moomers combie with each other to give the polymer. For example, a polymer may be obtaied from two moomers (A) ad (B) viz, A B A B or ( A B ) 407

22 MDULE Types of Polymers Soap, Detergets ad Polymers Depedig upo the ature of the repeatig structural uits (moomers), polymers are divided ito two broad categories viz., homopolymers ad copolymers (a) Homopolymer A polymer formed from oly oe kid of moomers is called homopolymer. Polyethee ( CH 2 CH 2 ) is a example of homopolymer. (b) Copolymer A polymer formed from more tha oe kid of moomer uits is called copolymer or mixed polymer. For example, Bua-S rubber which is formed from 1, 3- butadiee (CH 2 = CH CH = CH 2 ) ad styree (C 6 H 5 CH = CH 2 ) is a example of copolymer PLYMERIZATIN The process by which the moomers get liked up is called polymerizatio. Polymerizatio is represeted as : + M + M* M+M M M M M M M (M) M Dimer Trimer Polymer where M stads for the moomer Types of Polymerizatio Depedig upo the mode of reactio, polymerisatio is classified as : (a) additio polymerizatio ad (b) codesatio polymerizatio. (a) Additio Polymerizatio : This process ivolves the additio of moomer uits to themselves to form a growig chai by a chai reactio mechaism. It is for this reaso that the process is also kow as chai growth polymerizatio. Additio polymerizatio is achieved by addig a catalyst (kow as iitiator), which provides some reactive species like free radicals. For example bezoyl peroxide provides free radical bezyl to iitiate the chai polymerizatio reactio. H5C6 C C C 2C 6H 5 6H5 2C2 (orr) 408

23 Soap, Detergets ad Polymers Iitiatio R+ CH2 = CH2 R CH2 CH2 (Moomer) MDULE - 8 These free radicals (R) the attack the usaturated moomer ad form a ew free radical which goes o successively addig moomers ad thus grows the chai, this is called Chai propagatio : R CH 2 CH 2 +CH 2 =CH 2 R CH 2 CH 2 CH 2 CH 2 or M The fial termiatio of the two growig chais leads to a polymer. This is called chai termiatio : Codesatio Polymerizatio : I this, the moomers combie with the elimiatio of a small molecule like H 2, RH or NH 3, etc. The reactio is called (step growth) codesatio polymerizatio ad the product formed is called codesatio polymer. The process ivolves the elimiatio of by product molecules, therefore, the molecular mass of the polymer is ot the itegral multiple of the moomer uits. For example polyester or Terylee is a codesatio polymer of ethylee glycol ad terphthallic acid. H CH 2 CH 2 H + HC CH Ethelee glycol terphthallicacid H 2 CH 2 CH 2 C C Poly (ethylee terphthalate) or (Terylee) These two processes of makig polymers have several characteristics which distiguish them from each other. These are show i (Table 31.2). 409

24 MDULE - 8 Soap, Detergets ad Polymers Table 31.2 : Some differeces betwee additio polymerizatio ad codesatio polymerizatio Additio Polymerizatio Codesatio polymerizatio (Polycodesatio) 1. Ivolves usaturated 1. Ivolves substaces with at moomer like ethylee, viyl least 2 fuctioal groups like chloride, styree etc. ethylee glycol (2-H groups), adipic acid (2-CH groups). 2. Fast additio of moomers 2. Step-wise slow additio 3. At ay istat, oly moomer 3. No moomer. Mixtures of ad polymers are preset. dimers, trimers ad tetramers etc. are preset 4. Iitiator is ecessary to 4. Catalyst is ot ecessary. catalyse the polymerizatio. 5. No small molecules are elimiated. 5. Small molecules like H 2, HCl, C 2, CH 3 H are ofte elimiated. 6. Polymers are made for 6. Polymer are made for example, polyethee, example, terylee, ylo, polypropylee, polybutadiee, Formaldehyde-resis, silicoes. polyviylchloride. INTEXT QUESTINS Defie the terms : (i) Polymer (ii) Moomer 2. Write oe example of each of : (i) Additio polymerizatio (ii) Codesatio polymerizatio. 3. Differetiate betwee homopolymers ad copolymers. 4. Write moomers of Terylee ad Nylo CLASSIFICATIN F PLYMERS The polymers ca be classified i a umber of ways. Some of these are discussed below for a systematic ivestigatio of their properties ad uses. (a) Classificatio of Polymers o the Basis of rigi. the basis of origi, polymers are classified as : 410

25 Soap, Detergets ad Polymers 1. Natural polymers 2. Sythetic polymers 1. Natural Polymers : The polymers obtaied from ature (plats ad aimals) are called atural polymers. Starch, cellulose, atural rubber, proteis, etc. are some examples. 2. Sythetic Polymers : The polymers which are prepared i the laboratories are called sythetic polymers. These are also called ma-made polymers. Polyethee, PVC, ylo, feflo, bakelite, terylee, sythetic rubber, etc. are commo examples. (b) Classificatio of Polymers o the Basis of structure the basis of structure of polymers, these ca be classified as : 1. Liear polymers 2. Brached chai polymers 3. Cross-liked polymers. 1. Liear polymers : These are polymers i which moomeric uits are liked together to form liear chais. These liear polymers are well packed (Fig. 31.1) ad therefore, have high desities, high tesile (pullig) stregth ad high meltig poits. For example, polyethelee, ylos ad polyesters are examples of liear polymers. MDULE - 8 Fig : Liear Polymers Fig : Brached chai polymers 2. Brached chai polymers : These are polymers i which the moomers are joied to form log chai with side chais or braches of differet legths (Fig. 31.2). These brached chais polymers are irregularly packed ad therefore, they have lower tesile stregth ad meltig poits tha liear polymers. For example, low desity polyethee, glycoge, starch, etc. 3. Cross-liked polymers : These are polymers i which log polymer chais are cross-liked together to from a three dimesioal etwork. These polymers are hard, rigid ad brittle because of the etwork structure. (Fig bakelite, melamie ad formaldehyde resi are some examples of this type. 411

26 MDULE - 8 Soap, Detergets ad Polymers Fig : Cross liked polymers (c) Classificatio of Polymers o the Basis of Method of Polymerisatio the basis of method of polymerisatio the polymers are classified as : 1. Additio polymer : A polymer formed by direct additio of repeated moomers without the elimiatio of ay small molecule is called additio polymer. I this type, the moomers are usaturated compouds ad are geerally derivatives of ethee. The additio polymers have the same empirical formula as their moomers. Examples are polyethee, polypropylee ad polyviyl chloride, etc. 2. Codesatio polymer : A polymer formed by the codesatio of two or more tha two moomers with the elimiatio of simple molecules like water, ammoia, hydroge chloride, alcohol, etc. is called codesatio polymer. I this type, each moomer geerally cotais two fuctioal groups. For example, ylo 66 is obtaied by the codesatio of two moomers; hexa methyleediamie ad adipic acid with the loss of water molecules. H 2 H 2 N (CH 2 ) 6 NH 2 + HC (CH 2 ) 4 CH (NH (CH 2 ) 6 NH C (CH 2 ) 4 C ) ylo - 66 I this polymerizatio reactio NH 2 group of hexamethyleediamie reacts with CH group of adipic acid formig NH C likage with the elimiatio of H 2. H N H+H C H2 H N C likage Examples of codesatio polymers are Nylo 66, terylee, bakelite, alkylresis, etc. (d) Classificatio of Polymers o the Basis of Molecular Forces Depedig upo the itermolecular forces betwee moomer molecules, the polymers have bee classified ito four types. 412

27 Soap, Detergets ad Polymers 1. Elastomers 2. Fibers 3. Thermoplastics 4. Thermosettig 1. Elastomers : I case of elastomers the polymer chais are held together by weak va der waals forces. Due to weak forces, the polymers ca be easily stretched o applyig small stress ad they regai their origial shape whe the stress is removed. This is due to the presece of few- cross liks betwee the chais, which help the polymer to retract to its origial positio after the force is removed, as i vulcaized rubber. MDULE - 8 The most importat example of elastomer is atural rubber. 2. Fibres : These are the polymers which have strog itermolecular forces betwee the chais. These forces are either hydroge bods or dipole-dipole iteractios. Because of the strog forces, the chais are closely packed, givig them high tesile stregth ad less elasticity. These polymers ca be draw ito log, thi ad thread like fibres ad therefore ca be wove ito fabrics. The commo examples are ylo-66, dacro, silk, etc. 3. Thermoplastics : These are liear polymers with very few cross likages or o cross likages at all. The polymeric chais are held by weak VANDER WAAL forces ad slide over oe aother. Due to lack of cross likages these polymers softe o heatig ad harde or become rigid o coolig. Thus they ca be moulded to ay shape. Polythee, PVC, polystyree are additio type thermoplastics ad Terylee, ylo are codesatio type thermoplastics. Plasticizers : Certai plastics do ot softe much o heatig. These ca be easily softeed by the additio of some orgaic compouds which are called plasticizers. For example, polyviyl chloride (PVC) is very stiff ad hard but is made soft by addig di--butylphthalate (a plasticizer). Some other commo plasticizers are dialkyl phthalates ad cresyl phthalate. 4. Thermosettig polymers : Usually thermosettig polymer ca be heated oly oce whe it permaetly sets ito a solid which ca ot be remelted ad remoulded. Thermosettig polymers are produced from relatively low molecular mass semi fluid polymers (called polymers) which o heatig develop extesive cross-likage by themselves or by addig some cross-likig agets ad become ifusible ad isoluble hard mass. The cross liks hold the molecules i place so that heatig does ot allow them to move freely. Therefore, a thermosettig plastic is cross liked ad is permaetly rigid. The commo example are bakelite, melamie, formaldehyde resi, etc. Some importat differeces i the properties of thermosettig ad thermoplastic polymers are summerized i Table

28 MDULE - 8 Soap, Detergets ad Polymers Table 31.3 : Distictio betwee Thermoplastic ad Thermosettig polymers Themoplastic Thermosettig polymers 1. Liear Polymers. 1. Cross-liked polymers. 2. Weak va der Waals 2. Chemical cross-likig make itermolecular forces ad them ifusible materials. thus softe/melt o heatig. Do ot melt o heatig. 3. Molte polymer ca be 3. Cross-likig is usually moulded i desired shape. developed at the time of It ca be remoulded by mouldig where they heatig agai. harde irreversibly. 4. Examples are polystyree, 4. Examples are Glyptals, PVC, SBR, Teflo, PMMA epoxy polymers, terylee. formaldehyde resis. INTEXT QUESTINS Defie atural ad sythetic polymers with examples? 2. What are cross liked polymers? Give oe example of this type. 3. How do thermoplastic differ from thermosettig polymers? 4. Arrage the followig polymers i the icreasig order of their itermolecular forces. Also classify them as additio ad codesatio polymers. Nylo 66, Bua-S, Polyethee SME CMMERCIALLY IMPRTANT PLYMERS Polydies These polymers are obtaied whe a usaturated hydrocarbo with two double bods or whe a diee (2 double bod compoud) is polymerized with a substituted alkee. The polymers belogig to this class are rubbers or elastomer. They ca be atural or artificial. Cosequetly we have atural rubber ad sythetic rubber. (1) Natural Rubber : It is a polymer of usaturated hydocarbo, 2-methyl-1, 3- butadiee also called isopree. It is obtaied from the latex of rubber trees foud i tropical ad semi-tropical coutries such as Idia (souther part), Idoesia, Malayasia, Ceylo, South America, etc. The latex cotais about 25-40% of rubber hydrocarbos dispersed i water alogwith stabilizer proteis ad some fattyacids. It is a atural polymer ad possess remarkable elasticity. CH 2 =C CH=CH 2 CH 3 Isopree 2-methyl 1, 3 butadiee Polymerisatio CH 2 C=CH CH 2 CH 3 Polyisopree (atural rubber) 414

29 Soap, Detergets ad Polymers I atural rubber 10,000 to 20,000 isopree uits are liked together. MDULE - 8 Drawbacks of raw rubber Raw atural rubber has a umber of drawbacks. For example : 1. Rubber is brittle at low temperature ad becomes very soft at high temperatures. Thus it ca be used oly i the limited temperature rage of C 2. It is too soft to be used for heavy duty operatio. 3. stretchig, it udergoes permaet deformatio. 4. Not resistat to mieral oils, orgaic solvets ad eve actio of water. It has large water absorptio capacity. Vulcaizatio of Rubber The wide applicatios of rubber are due to its property called elasticity ad that is why rubber is said to be a elastoplastic or elastomer. Accidetally, i 1893, Charles Goodyears discovered that additio of sulphur to hot rubber cause chages that improve its physical properties i a spectacular maer. This process is called vulcaizatio. It is carried out by heatig crude rubber i presece of sulphur or dippig it i a solutio of S 2 Cl 2 i CS 2. Vulcaisatio depeds upo : (i) The amout of sulphur used : by icreasig the amout of sulphur rubber ca be hardeed (ii) Temperature (iii) Duratio of heatig. Crude rubber is itimately mixed with about 3% groud sulphur, a accelerator ad activator ad the heated to about C (for tyres it is C). Vulcaisatio is a progressive reactio ad is allowed to a defiite stage. The detailed mode of vulcaizatio process may be difficult to visualize, but probable structure of vulcaized rubber is depicted below (Fig. 33.4). Sulphur Heat Natural rubber Vulcaized rubber Fig : Process of vulcaizatio of rubber 415

30 MDULE - 8 Soap, Detergets ad Polymers Table 31.4 Compariso of some properties of atural rubber ad vulcaized rubber : Natural Rubber Vulcaised rubber 1. Natural rubber is soft ad 1. Vulcaized rubber is hard ad sticky. o-sticky. 2. It has low tesile stregth. 2. It has high tesile stregth. 3. It has low elasticity. 3. It has high elasticity. 4. It ca be used over a arrow 4. It ca be used over a wide rage of temperature (from 10 0 rage of temperature ( to to 60 0 C) C). 5. It has low wear ad tear 5. It has high wear ad tear resistace. resistace. 6. It is soluble i solvets like 6. It is isoluble i most of the ether, carbo tetrachloride, commo solvets. petrol, etc. (2) Sythetic Rubbers Sythetic high polymers possessig similar physical properties as that of atural rubber are called sythetic rubber. Usually sythetic rubber is a improvemet over atural rubber, specially with respect to its resistace to oils, gas, solvets. Some sythetic rubbers are made by polymerizatio of oly oe moomer, for example Neopree is made by polymerizatio of chloropree, while sythetic rubbers like Bua-S, Bua N ad Butyl rubber etc. are copolymers as these have more the oe moomer. Neopree : This sythetic rubber resembles atural rubber i its properties. It is obtaied by polymerizatio of chloropree. CH 2 =C CH=CH 2 CH2 C CH CH2 Cl Cl Chloropree eopree Chloropree is obtaied by the reactio of HCl with viylacetylee CH 2 =CH C Viyl acetylee CH + HCl CH 2 =CH C=CH 2 Cl Chloropree Neopree is superior to atural rubber i its stability to aerial oxidatio ad its resistace to oils, gasolie ad other solvets Neopree is used for (i) makig belts, hoses, shoe heals, stoppers, etc. ad (ii) maufacture of cotaiers for storig petrol, oil ad other solvets. 416

31 Soap, Detergets ad Polymers Bua S: It is obtaied by polymerizatio of butadiee ad styree i presece of sodium metal. CH 2 =CH CH=CH 2 +CH=CH 2 butadiee C 6 H 5 Styree Na Heat MDULE - 8 ( CH 2 CH=CH CH 2 CH CH 2 ) C 6 H 5 Bua S I Bua S, Bu stads for butadiee, Na for sodium ad S stads for styree. It is also called S.B.R. (Styree Butadiee Rubber). It has slightly less tesile stregth tha atural rubber. Bua-S is used for (i) makig automobile tyres. (ii) rubber soles, belts ad hoses etc. Bua N : It is obtaied by copolymerizatio of two parts of butadiee ad oe part of acryloitrile i presece of sodium metal. Bua N is hard ad extremely resistat to the swellig actio by oils (petrol), solvets ad is resistat to heat, etc. Uses : (i) It is used for the maufacture of storage taks for solvets ad (ii) For makig oil seals. Butyl Rubber : This is obtaied as a result of co-polymerizatio of butadiee ad isobutylee. It is geerally carried out i the presece of small quatity of isopree. The fuctio of isopree is ot exactly kow. CH = CH CH = CH + (CH ) C = CH butadiee iso-butylee ( CH CH CH CH C CH ) (CH ) butylrubber Butyl rubbers are iert towards acids ad alkalies, but have poor resistace towards petroleum products. 417