Organic Chemical Compounds

Transcription

1 Organic Chemical Cmpunds Objective: There are millins f knwn carbn cmpunds. In this experiment, several f the majr families f carbn cmpunds will be investigated, which will demnstrate sme f the characteristic prperties and reactins f each family. Intrductin: Carbn atms have the crrect electrnic cnfiguratin and size t enable lng chains r rings f carbn atms t be built up. This ability t frm lng chains is unique amng the elements, and is called catenatin. There are knwn mlecules that cntain thusands f carbn atms, all f which are attached by cvalent bnds amng the carbn atms. N ther element is able t cnstruct such large mlecules with its wn kind. Hydrcarbns: The simplest types f carbn cmpunds are knwn as hydrcarbns. Such mlecules cntain nly carbn atms and hydrgen atms. There are varius srts f mlecules amng the hydrcarbns, differing in the arrangement f the carbn atms in the mlecule, r in the bnd between the carbn atms. Hydrcarbns cnsisting f chain-like arrangements f carbn atms are called aliphatic hydrcarbns, whereas mlecules cntaining the carbn atms in a clsed ring shape are called cyclic hydrcarbns. Fr example, the mlecules hexane and cyclhexane represent aliphatic and cyclic mlecules, each with six carbn atms: Hexane image Cyclhexane image Ntice that all the bnds between carbn atms in hexane and cyclhexane are single bnds. Mlecules cntaining nly singly bnded carbn atms are said t be saturated. Other mlecules are Other mlecules are knwn in which sme f the carbn atms may be attached by duble r even triple bnds and are said t be unsaturated. The fllwing are representatins f the mlecules 1-hexene and cyclhexene, which cntain duble bnds: 1-hexene image cyclhexene Hydrcarbns with nly single bnds are nt very reactive. One reactin all hydrcarbns underg, hwever, is cmbustin. Hydrcarbns react with xygen, releasing heat and/r light. Fr example, the simplest hydrcarbn is methane, CH 4, which cnstitutes the majr prtin f natural gas. Methane burns in air, prducing carbns dixide, water vapr, and heat: CH CO 2 + 2H 2 O Single-bnded hydrcarbns als will react slwly with the halgen elements (chlrine and brmine). A halgen atm replaces ne r mre f the hydrgen atms f the hydrcarbns. Fr example, if methane is treated with brmine, brmmethane is prduced, with cncurrent release f hydrgen brmide: CH 4 + Br 2 CH 3 Br + HBr The hydrgen brmide prduced is generally visible as a fg evlving frm te reactin cntainer, prduced as the HBr mixes with water vapr in the atmsphere. Mlecule with duble and triple bnds are much mre reactive than single-bnded cmpunds. Unsaturated hydrcarbns underg reactins at the site f the duble r triple bnd, in which the fragments f sme utside reagent attach themselves t the carbn atms that had been invlved in the duble r triple bnd. Such reactins are called additin reactins. The rbitals f the carbns atms that had been used fr the extra bnd instead are used fr attaching the fragments f the new reagent. Fr example, the duble-bnded cmpund ethylene will react with many reagents: CH 2 CH 2 + H 2 CH 3 CH 3 CH 2 CH 2 + HBr CH 3 CH 2 Br CH 2 CH 2 + H 2 O CH 3 CH 2 OH CH 2 CH 2 + Br 2 CH 2 BrCH 2 Br

2 Ntice that in all f these reactins f ethylene, the prduct is saturated and n lnger cntains a duble bnd. Many f the reactins f t ethylene indicated nly take place in the presence f a catalyst, r under reactin cnditins that we will nt be able t investigate in this experiment. Cyclic cmpunds cntaining nly single r duble bnds underg basically the same reactins indicated earlier fr aliphatic hydrcarbns. One class f cyclic cmpunds, called the armatic hydrcarbns, have unique prperties that differ markedly frm thse we have discussed. The parent cmpund f this grup f hydrcarbns is benzene: Benzene images Althugh we typically draw the structure f benzene indicating duble bnds arund the ring f carbn atms, in terms f its reactins, benzene behaves as thugh it did nt have any duble bnds. Fr example, if elemental brmine is added t benzene (with suitable catalyst), benzene des nt underg additin reactin as wuld be expected fr a cmpund with duble bnds. Rather, it underges a substitutin reactin f the srt that wuld be expected fr single-bnded hydrcarbns: Benzene image Brmbenzene This reactin indicates that perhaps benzene des nt have any duble bnds in reality. Several Lewis dt structures can be drawn fr benzene, with the duble bnds in several different lcatins in the ring. Benzene exhibits the phenmenn f resnance; that is, the structure f benzene shwn, as well as any ther structure that might be drawn n paper, des nt really represent the true electrnic structure f benzene. The electrns f the duble bnds f the benzene are, in fact, delcalized arund the entire ring f the mlecule and are nt cncentrated in any particular bnds between carbn atms. The ring structure f the benzene is part f many rganic mlecules, including sme very cmmn bilgical cmpunds. Functinal Grups While the hydrcarbns just described are f interest, the chemistry f rganic cmpunds cntaining atms ther than carbn and hydrgen is far mre varied. When anther atm, r grup f atms, is added t a hydrcarbns framewrk, the new atm frequently imparts its wn very strng characteristic prperties t the resulting mlecule. An atm r grup f atms that is able t impart new and characteristic prperties t an rganic mlecule is called a functinal grup. With millins f carbn cmpunds knwn, it has been helpful t chemists t divide these cmpunds int families, based n what functinal grup they cntain. Generally it is fund that all the members f a family cntaining a particular functinal grup will have many similar physical prperties and will underg similar chemical reactins. A. Alchls Simple hydrcarbn chains r rings that cntain a hydrxyl grup bnded t a carbn atm are called alchls. The fllwing are several: Methanl image Ethanl image 1-prpanl image The OH grup f alchls shuld nt be cnfused with the hydrxide in, OH -. Rather than being basic, the hydrxyl grup makes the alchls in many ways like water, H-OH. Fr example, the smaller alchls are fully miscible with water in all prprtins. Alchls are similar t water in that they als react with sdium, releasing hydrgen. Alchls, hwever, react mre slwly with sdium than des water. Many alchls can be xidized by reagents, such as permanganate ins r dichrmate ins, with the prduct depending n the structure f the alchl. Fr example, ethyl alchl is xidized t acetic acid: When wine spils, vinegar is prduced. On the ther hand, 2-prpanl is xidized t prpanne (acetne) by such xidizing agents: Ethanl image Acetic acid image 2-prpanl image Acetne Alchls are very imprtant in bichemistry, since many bilgical mlecules cntain the hydrxyl grup. Fr example, carbhydrates are alchls, with a particular mlecule generally cntaining several hydrxyl grups.

3 B. Aldehydes and Ketnes An xygen atm that is duble bnded t a carbns atm f a hydrcarbn chain is referred t as a carbnyl grup. Tw families f rganic cmpunds cntain the carbnyl functin, with the difference between the families having t d with where alng the chain f carbn atms the xygen atm is attached. Mlecules having the xygen atms attached t the first (terminal) carbn atm f the chain are called aldehydes, whereas mlecule having the xygen atm attached t an interir carbn atm are called ketnes. Aldehydes are intermediates in the xidatin f alchls. Fr example, when ethyl alchl is xidized, the prduct is first acetaldehyde, which is then further xidized t acetic acid: ethanl acetaldehyde acetic acid Ketnes are the end prduct f the xidatin f alchls in which the hydrxyl grup is attached t an interir carbn atm (called secndary alchls, as was indicated earlier fr 2-prpanl. Aldehydes and ketne are imprtant bilgically because all carbhydrates are als either aldehydes r ketnes, as well as being schwanzen (alchls). The cmmn sugars glucse and fructse are shwn next. Ntice that glucse is an aldehyde, whereas fructse cntains the ketne functinal grup. Glucse image Fructse image Mlecules such as glucse and fructse, which cntain bth carbnyl and hydrxyl functin, are easily xidized by Benedict s reagent. Benedict s reagent is a specially prepared slutin f cpper(ii) in that is reduced when added t certain sugars, prducing a precipitate f rep cpper(i) xide. Benedict s reagent is the basis fr the cmmn test fr sugars in the urine f diabetics. A strip f paper r tablet cntaining Benedict s reagent is added t a urine sample. The presence f sugars is cnfirmed if the clr f the test reagent changes t the clr f cpper(i) xide. Benedict s reagent reacts nly with aldehydes and ketnes that als cntain a crrectly lcated hydrxyl grup, but will nt react with simple aldehydes r ketnes. C. Organic Acids Mlecules that cntain the carbxyl grup at the end f a carbn atm chain behave as acids. Fr example, the hydrgen atm f the carbxyl grup f acetic acid inizes as: Acetic acid acetate in + hydrgen in On paper, the carbxyl grup lks like a crss between the carbnyl grup f aldehydes and the hydrxyl grup f alchls, but the prperties f the carbxyl grup are cmpletely different frm either f these. The hydrgen atm f the carbxyl grup is lst by rganic acids because the remaining in has mre than ne pssible resnance frm, which leads t increased stability fr this in, relative t the nninized mlecule. Organic acids are typically weak acids, with nly a few f the mlecules in a sample being inized at any given time. Hwever, rganic acids are strng enugh t react with bicarbnate ins r t cause an acidic respnse in ph test papers r indicatrs.

4 D. Organic Bases There are several types f rganic cmpunds that shw basic prperties, the mst ntable f such cmpunds frming the family f amines. Amines are cnsidered t be rganic derivatives f the weak base ammnia, in which ne r mre f the hydrgen atms f ammnia is replaced by chains r rings f carbn atms. The fllwing are sme typical amines: Ammnia image Methylamine image Dimethylamine image Ethyldimethylamine image Like ammnia, rganic amines react with water, releasing hydrxide ins frm water mlecules: NH 3 +H 2 O NH 4 + +OH - CH 3 NH 2 +H 2 O CH 3 NH 3 + +OH - Althugh amines are weak bases (nt fully dissciated), they are basic enugh t cause a clr change in ph test paper and indicatrs, and are able t cmplex many metal ins in a similar manner t ammnia. The s-called amin grup, -NH 2, fund in sme amines (primary amines) is als present in the class f bilgical cmpunds called amin acids. Many f the amin acids frm which prteins are cnstructed are remarkably simple, cnsidering the verall cmplexity f prteins. The amin acids fund in human prtein cntain a carbxyl grup, whit an amin grup attached t the carbn atm next t the carbxyl grup in the mlecule s carbn chain. This srt f amin acid is referred t as an alpha amin acid. One simple amin acid fund in human prtein is shwn her: Glycine (2-aminethanic acid) Safety Precautins Safety eyewear apprved by yur institutin must be wrn at all times while yu are in the labratry, whether r nt yu are wrking n an experiment. Assume that all the rganic substances are highly flammable. Use nly small quantities, and keep them away frm pen flames. Use a ht water bath if a surce f heat is required. Assume that all substances are txic and are capable f being absrbed thrugh the skin. Avid cntact and wash after use. Infrm the instructr f any spills. Assume that the vapr f all rganic substances are harmful. Use small quantities and wrk in the fume exhaust hd. Sdium reacts vilently with water, liberating hydrgen gas and enugh heat t ignite the hydrgen. D nt dispse f sdium in the sinks. Add any excess sdium t a small amunt f ethyl alchl, and allw the sdium t react fully with the alchl befre dispsal. Ptassium permanganate, ptassium dichrmate, and Benedict s reagent are txic. Permanganate and dichrmate can harm skin and clthing. Exercise cautin and wash after use. Chrmium cmpunds are suspected mutagens/carcingens. Brmine causes extremely bad burns t skin, and its vaprs are extremely txic. Wrk with brmine nly in the fume exhaust hd, and handle the bttle with a twel while dispensing. Dispse f all materials as directed by the instructr. Apparatus/Reagents Required Hexane, 1-hexane, cyclhexane, cyclhexene, tluene, ethyl alchl, methyl alchl, isprpyl alchl, n- butyl alchl, n-pentyl alchl, n-ctyl alchl, 10% frmaldehyde slutin, 10% acetaldehyde slutin, acetne, 10% glucse, 10% fructse, acetic acid, prpinic acid, butyric acid, ammnia, 10% butylamine, 1% brmine in methylene chlride, 1% aqueus ptassium permanganate, Benedict s reagent, sdium pellets, 5% acidified ptassium dichrmate slutin, ph paper, 10% sdium bicarbnate slutin, 1M cpper sulfate slutin

5 Prcedure Recrd all data and bservatins directly n the reprt pages in ink. A. Hydrcarbns Yur instructr will ignite small prtins f hexane, 1-hexene, cyclhexene, and tluene t demnstrate that they burn readily (d nt attempt this yurself). Ntice that tluene (an armatic cmpund) burns with a much stier flame than the ther hydrcarbns. This is characteristic f armatics. Obtain small (0.5mL) prtins f hexane, 1-hexene, cyclhexene, and tluene in separate small test tubes. Take the test tubes t the exhaust hd, and add a few drps f 1% brmine t each. Thse samples cntaining duble bnds will declrize the brmine immediately (additin reactin). Thse sample that did nt declrize the brmine immediately will gradually lse the brmine clr (substitutin reactin). B. Alchls Obtain small samples f methyl, ethyl, isprpyl, n-butyl, n-pentyl, and n-ctyl alchls in separate clean test tubes. Add an equal quantity f distilled water t each test tube, stpper, and shake. Recrd the slubility f the alchls in water. In alchls with nly a few carbn atms, the hydrxyl grup cntributes a majr prtin f the mlecule s physical prperties, making such alchls miscible with water. As the carbn atm chain f an alchl gets larger, the alchl becmes mre hydrcarbn in nature and less sluble in water. Obtain 2 drp samples f methyl, ethyl, isprpyl, n-butyl, n-pentyl, and n-ctyl alchls in separate clean test tubes. Wearing dispsable glves, add 10 drps f acidified ptassium dichrmate t each sample, transfer t a ht water bath, and heat until a reactin is evident. Dichrmate ins xidize primary and secndary alchls. Obtain small samples f methyl, ethyl, isprpyl, n-butyl, n-pentyl, and n-ctyl alchls in separate clean test tubes. Have the instructr add a tiny pellet f sdium t each test tube. The vigr f the reactin depends n the structure f the alchl. Smaller alchls are mre reactive than larger alchls. Wait until all the sdium in the test tubes have cmpletely reacted. Then add abut 5mL f distilled water t the test tubes, and test the resulting slutin with ph paper. The alkxide in that remains frm the alchls after the reactin with the sdium is strngly basic in aqueus slutin. C. Aldehydes and Ketnes Obtain 2 drp samples f frmaldehyde, acetaldehyde, acetne, glucse, and fructse in separate test tubes. Wearing glves, add 10 drps f acidified ptassium dichrmate slutin t each sample, and transfer the test tubes t a ht water bath. Aldehydes are xidized by dichrmate, being cnverted int rganic acids. Recrd which samples change clr. Obtain small samples f frmaldehyde, acetaldehyde, acetne, glucse, and fructse in separate test tubes. T each test tube add 5mL f Benedict s reagent, and transfer t a ht water bath. Mlecules cntaining a hydrxyl grup next t a carbnyl grup n a carbn atm chain will cause a clr change in Benedict s reagent. This test is applied t urine fr the detectin f sugar. D. Organic Acids Obtain small samples f acetic acid, prpinic acid, and butyric acid in separate small test tubes. Add 5mL f 10% sdium bicarbnate slutin t each test tube: a marked fizzing will result as the acids release carbn dixide frm the bicarbnate. Obtain small samples f acetic acid, prpinic acid, and butyric acid in separate small test tubes. Add 5mL f water t each test tube, and test the slutin with ph paper.

6 E. Organic Bases Obtain small samples f aqueus ammnia and f n-butylamine slutin in separate small test tubes. Determine the ph f each sample with ph test paper. Add a few drps f 1M cpper sulfate slutin t each test tube and shake. The clr f the cpper sulfate slutin shuld darken as the metal/amine cmplex is frmed.

7 Organic Chemical Cmpunds Pre-Labratry Questins Draw the structural frmulas fr each f the fllwing substances. If the cmmn name f the substances is given write the IUPAC name fr the substance. hexane isprpyl alchl 1-hexene frmaldehyde cyclhexane acetaldehyde cyclhexene acetne tluene acetic acid methyl alchl butyric acid ethyl alchl n-butylamine Results/Observatins A. Hydrcarbns Observatins f igniting Which cmpunds declrized brmine immediately? Which cmpunds declrized brmine n expsure t light?

8 Which cmpunds prduced an HBr fg? Which cmpunds caused a clr change in KmnO 4? B. Alchls Which alchls were fully sluble in water? Which alchls caused a clr change when tested with dichrmate in? Relative vigr f reactin f alchls with sdium Apprximate ph f water slutins f alchl/sdium prduct C. Aldehydes and Ketnes Which aldehydes/ketnes caused a clr change when tested with dichrmate in? Which aldedhydes/ketnes caused a clr change when tested with Benedict s reagent? D. Organic Acids Observatins n test with bicarbnate Apprximate ph f aqueus slutin f rganic acid samples E. Organic Bases Apprximate ph f aqueus slutins f ammnia/n-butylamine Observatins f adding CuSO 4 Questins 1. When sdium bicarbnate was added t an rganic acid sample, carbn dixide was evlved. Is this test specific fr rganic acids, r des it apply t acids in general? Write the balanced equatin fr the prcess.