Directed by Ph. Sadeel Shanshal

Transcription

1 University of Mosul College of Pharmacy Practical Laboratory Dept. of Pharmaceutical Chemistry Head of dept. Dr. Nohad Al.Omari Directed by Ph. Sadeel Shanshal

2 Experiment No.1 Identification of Carboxylic Acids Carboxylic acids are organic compounds that have a carboxyl group attached to an alkyl group (RCOOH) or to an arylgroup (ArCOOH). The 'R' may be a hydrogen and the result is formic acid. They may be mono carboxylated, multi carboxylated, substituted (e. g., hydroxyl groups), or they may be aromatic.

3 Physical properties : Only formic acid, acetic acid, and lactic acid are liquids at room temperature. The others are solids. Low molecular weight carboxylic acids are soluble in water and, therefore, lie under class S 1. Water insoluble acids dissolve in both sodium hydroxide solution and sodium bicarbonate solution, being classified under class A 1. When they react with sodium bicarbonate, they evolve carbon dioxide gas. This is considered as a good simple indication of them. Their boiling points are generally high due to the association through hydrogen bonds: two molecules of the carboxylic acid are held together by two hydrogen bonds rather than one. Aromatic carboxylic acids burn with a yellow smoky flame whereas aliphatic ones burn with a blue flame without smoke. Chemical properties : The acidic properties of carboxylic acids are attributed to the proton of the carboxyl group. Mono carboxylic acids are weak acids except formic acid, which is the strongest. The tendency of the alkyl group to release electrons weakens the acid; thus formic acid is the strongest. On the other hand presence of electron withdrawing groups (such as halogens) especially on the alpha carbon increases the acidity.

4 Reactions of carboxylic acids are related to : the proton as in salt formation reactions. removal of the hydroxyl group as in conversion to derivatives such as esters, amides, or acid chlorides. substitution either in the alpha position of aliphatic acids or in the meta position of aromatic ones. Chemical reactions : 1. General test (Ferric chloride test) The acid solution should be made neutral before performing the test with ferric chloride solution. This is achieved by adding very dilute ammonia solution drop by drop with shaking to a solution of about 0.5 g of the solid acid or 2 drops of the liquid acid in 1 ml water until the medium becomes basic as indicated by changing the colour of litmus paper to blue or changing the colour of phenolphthalein indicator from colorless to pink, in which case the characteristic odour of ammonia is predominant. At this stage the solution is slightly basic. To make the solution neutral the excess ammonia should be removed by gently heating the test tube in a water bath with shaking from time to time until both the odour of ammonia and the pink colour disappears. (In case of oxalic, tartaric, citric and lactic acids keep a portion of their neutral solution for use in calcium chloride test). Cool the solution and then add few drops of ferric chloride solution to get different colours (solutions or precipitates) as follows :

5

6 Therefore elimination of the excess ammonia is important since the brown orange precipitate of ferric hydroxide formed by this excess interferes with the colour of the ferric salt of the acid resulting in a false result. If the solution is still acidic (little ammonia is added), colourless complexes are formed between the acid and ferric ions, a false negative result. As mentioned in the above table formic acid and acetic acid form a red coloured solution in this test : Succinic acid and benzoic acid give a light brown precipitate:

7 To distinguish between these two acids add few drops of dilute sulphuric acid to this light brown precipitate with shaking thereby liberating the free carboxylic acid back. If the liberated acid is water soluble then it is succinic acid which is aliphatic. On the other hand benzoic acid is liberated as a white precipitate because it is insoluble in water since it is aromatic. Salicylic acid gives a violet colour:

8 2. Special tests for formic acid Since formic acid has a hydrogen attached to the carbonyl group (HC=O) it can reduce certain compounds while being oxidized : a) Reduction of mercuric chloride Formic acid reduces mercuric chloride to mercurous chloride in the form of white precipitate and, in the presence of excess acid, mercurous chloride is reduced to mercury element as a gray precipitate. To few drops of the acid add few drops of mercuric chloride solution, and then heat to get a white precipitate. Add excess of the acid with heating to get the gray precipitate of elemental mercury. b) Tollen's test Refer to the experiment of identification of aldehydes and ketons for preparation of Tollen's reagent and procedure of this test.

9 c) Alkaline potassium permanganate test Formic acid reacts with potassium permanganate solution, a strong oxidizing agent, in alkaline medium causing decolourization of this violet reagent. Mix 2 3 drops of the acid with 5 ml of sodium bicarbonate solution, and then add 1 % potassium permanganate solution drop by drop and observe the disappearance of the original violet colour of the reagent which will be followed by the appearance of a brown precipitate of manganese dioxide. 3. Special test for acetic acid (ester formation) Acetic acid, on contrary to formic acid, neither can be oxidized by, nor can reduce any of the reagents applied to formic acid. Instead, it undergoes ester formation reaction : Mix 1 ml of acetic acid with 2 ml of ethanol in a test tube and add to this mixture 2 3 drops of concentrated sulphuric acid. Heat the test tube in a water bath for 10 minutes, and then pour the mixture into another test tube containing 5 ml sodium bicarbonate solution; the characteristic fruity odour of ethyl acetate can be smelt, which indicates the formation of this ester.

10 4. Special test for succinic acid (Fluorescence test) In a dry test tube mix equal quantities of succinic acid and resorcinol with 2 drops of concentrated sulphuric acid. Heat the mixture on direct flame for 1 minute until the mixture melts. Cool and add excess of 10 % sodium hydroxide solution to get a red colour with green fluorescence. If the colour is not so clear dilute with water. 5. Special tests for tartaric acid a) Reaction with concentrated sulphuric acid When a mixture of about 0.5 g of tartaric acid and 1 ml of concentrated sulphuric acid is heated gently on a flame with shaking heavy charring takes place and carbon monoxide, carbon dioxide, sulphur dioxide gases are evolved.

11 b) Reaction with calcium chloride solution To about 1 ml of the cold neutral solution of the tartaric acid (see the general test) add few drops of calcium chloride solution; a white precipitate of calcium tartrate is formed. This precipitate dissolves in dilute hydrochloric acid but not in dilute acetic acid. c) Reaction with Fenton's reagent Dissolve about 0.5 g of tartaric acid in 1 ml of water and then add 1 drop of ferrous sulphate solution followed by 2 drops of hydrogen peroxide solution. Then add excess of 10 % sodium hydroxide solution until an intense violet colour is observed.

12 In this reaction the components of Fenton's reagent (hydrogen peroxide and iron) undergo an oxidation-reduction reaction that results in the generation of ferric ions which form ferric salt of dihydroxyfumaric acid that is responsible for the violet colour. 6. Special tests for oxalic acid a) Reaction with potassium permanganate solution Oxalic acid reacts with acidic potassium permanganate solution causing decolourization of this reagent. It doesn't react with this reagent under alkaline medium. Dissolve 0.5 gm of the acid in 2 3 ml of distilled water and add 2 3 ml of dilute sulfuric acid. Heat gently (water bath), and then add potassium permanganate solution drop by drop and observe the disappearance of the violet color of the reagent. b) Reaction with calcium chloride solution For procedure follow the same steps mentioned above for tartaric acid. The same results are obtained. c) Reaction with concentrated sulphuric acid For procedure follow the same steps mentioned above for tartaric acid. The same gases are bubbled out with a little darkening.

13 d) Reaction with Fenton's reagent For procedure follow the same steps mentioned above for tartaric acid. Oxalic acid gives negative result with this reagent. 7. Special tests for lactic acid a) Iodoform test Lactic acid can undergo iodoform formation reaction since it contains a free methyl group and a hydrogen attached to the carbon bearing the hydroxyl group: For procedure follow the same steps mentioned in the identification of alcohols experiment. b) Reaction with concentrated sulphuric acid For procedure follow the same steps mentioned above for tartaric acid. The same gases are bubbled out with a considerable blackening but without a marked charring. c) Reaction with calcium chloride solution For procedure follow the same steps mentioned above for tartaric acid. Lactic acid gives negative result.

14 d) Reaction with Fenton's reagent For procedure follow the same steps mentioned above for tartaric acid. Lactic acid gives negative result with this reagent. 8. Special tests for citric acid a) Reaction with concentrated sulphuric acid For procedure follow the same steps mentioned above for tartaric acid. The same gases are bubbled out and the mixture turns to yellow but does not char. Acetone dicarboxylic acid is also formed, and its presence is tested by heating the mixture for 1 minute, cool, add a few mls of water and make alkaline with 30% sodium hydroxide solution. Add a few mls of sodium nitroprusside solution and observe the intense red colouration of the medium. b) Reaction with calcium chloride solution For procedure follow the same steps mentioned above for tartaric acid. Citric acid gives the same results. c) Reaction with Fenton's reagent For procedure follow the same steps mentioned above for tartaric acid. Citric acid gives negative result with this reagent.

15 9. Special test for salicylic acid (ester formation) In addition to the characteristic violet colour obtained with ferric chloride, salicylic acid can also be detected by ester formation test. In this test methyl salicylate ester separates out as an organic phase having a characteristic odour. Follow the same procedure and conditions used for esterification of acetic acid but use methanol instead of ethanol. Note that methanol is toxic internally so never withdraw it by mouth to avoid accidental ingestion.

16 Experiment No.2 Identification of Carboxylic Acids Salts Carboxylic acids salts are organic compounds with the general formula (RCOOM) where (RCOO-) refers to the carboxylic acid part and (M+) is the alkali part which, in this experiment, may be either a metal cation (Na+ or K+) or ammonium (NH4+). These salts are colourless or white crystalline solids and are soluble in cold or hot water. Identification of the carboxylic acid part (anionic part) The carboxylic acid part can be identified by the usual steps for identification of carboxylic acids starting with ferric chloride test and, according to the result observed, the proper special test should be performed then to conclude the carboxylate name (formate, lactate, salicylate, etc.).

17 Identification of the alkali part (cationic part) Identification of sodium or potassium cations Place about 0.1 g of the salt on the edge of a metal spatula and start heating it gently on a flame with gradual increase in the heat strength. Sodium and potassium salts leave a residual amount of solid on the spatula in addition to the carbon coming from decomposition of the organic part. This residual solid may be sodium carbonate or potassium carbonate and can be detected, after cooling, by the addition of few drops of dilute hydrochloric acid solution which results in a strong effervescence within the residual solid due to liberation of carbon dioxide gas : During ignition observe the colour of the flame. Sodium salts burn with a golden yellow flame whereas potassium salts burn with a purple flame. Identification of ammonium cation Repeat the ignition procedure mentioned above and note that ammonium salts don't leave any residual solid except the carbon coming from decomposition of the organic part. After cooling, addition of few drops of dilute hydrochloric acid does not result in any effervescence. Ammonium cation can be detected as follows. Place few crystals of the salt in a test tube and add 0.5 ml of 10 % sodium hydroxide solution. At this stage free ammonia is liberated and can be smelt easily:

18 Place a small filter paper over the top of the tube and fold it down around the tube. Add 2 drops of 10 % copper sulphate solution on the filter paper covering the mouth of the test tube. Heat the test tube mildly on a flame to boil the mixture. The liberated ammonia will react with the copper ions present on the filter paper resulting in a blue colour.

19 Experiment No.3 Identification Of Amines Amines are basic organic compounds that are considered as derivatives of ammonia. They are classified as primary, secondary, or tertiary according to the number of groups attached to the nitrogen atom: RNH 2, R 2 NH, or R 3 N respectively where R is any alkyl or aryl group.

20 Physical properties Like ammonia, amines are polar compounds and all of them can form intermolecular hydrogen bonds except tertiary amines. They have lower boiling points than alcohols or carboxylic acids of the same molecular weight but higher boiling points than non polar compounds. Methylamine is gas while o- phenylenediamine and p,p-diaminodiphenylmethane are solids. The others are liquids. All amines are capable of forming hydrogen bonds with water, thus those with six carbon atoms or less are quite soluble in water. They are soluble in organic solvents as ether, alcohol and benzene. All of them have fish like odour except the methylamines and ethylamines which smell just like ammonia. Aromatic amines are colourless when pure, but they are easily oxidized by air becoming coloured. They are generally very toxic and can be absorbed through the skin. Chemical reactions : All classes of amines (primary, secondary, and tertiary) have an unshared pair of electrons on the nitrogen atom, just like ammonia. That is why they are similar to ammonia in their chemical behavior (mainly basicity and neocleophilicity).

21 1. Ramini and Simon tests (Sodium nitroprusside tests). (conventional Ramini and Simon tests) In Ramini test the amine reacts with acetone and the product interacts with sodium nitroprusside (Na 2 [Fe(NO)(CN) 5 ].2H 2 O) that is dissolved in 50% aqueous methanolic solution to produce a coloured complex. In Simon test acetone is replaced by 2.5 M acetaldehyde solution. These two tests distinguish between primary and secondary aliphatic amines. To distinguish between aromatic amines (primary, secondary and tertiary) the modified Ramini and Simon tests are applied. These tests use the same reagents and procedure of the conventional tests but the modifications are the replacement of the methanolic solution of sodium nitroprusside by a solution of sodium nitroprusside in dimethylsulfoxide (modified sodium nitroprusside reagent) and the use of a saturated aqueous solution of zinc chloride instead of water. Procedure : Ramini test To 1 ml of methanolic sodium nitroprusside solution add 1 ml of distilled water, 5 drops of acetone, and about 30 mg of the amine. In most cases the characteristic colour appear in a few seconds, although in some cases 2 minutes may be necessary. Simon test Follow the above procedure exactly but use 5 drops of 2.5 M acetaldehyde solution instead of acetone. Up to 2 minutes may be needed for the colour to develop.

22 Modified Ramini test To 1 ml of the modified sodium nitroprusside reagent add 1 ml of saturated aqueous zinc chloride solution, 5 drops of acetone, and about 30 mg of the amine. Primary and secondary aromatic amines produce orange-red to red-brown colours within a period of few seconds to 5 minutes. Tertiary aromatic amines give a colour that changes from orange-red to green over a period of about 5 minutes. Modified Simon test Follow the above procedure exactly but use 5 drops of 2.5 M acetaldehyde solution instead of acetone. Primary aromatic amines give an orange-red to red-brown colour within 5 minutes; secondary aromatic amines give a colour changing from red to purple within 5 minutes; tertiary aromatic amines give a colour that changes from orange-red to green over a period of about 5 minutes. Examples are outlined in the following table:

23 2. Nitrous acid test The reaction of amines with nitrous acid (HNO 2 ) is another test that classifies the amine not only as primary, secondary, or tertiary, but also as aliphatic or aromatic. Primary aromatic and aliphatic amines react with nitrous acid to form an intermediate diazonium salt. The aliphatic diazonium salts decompose spontaneously by rapid loss of nitrogen, particularly when the original amino group is attached to a secondary or tertiary carbon, while most aromatic diazonium salts are stable at 0 C but lose nitrogen slowly on warming to room temperature. Secondary amines undergo a reaction with nitrous acid to form N-nitrosoamines, which are usually yellow oils or solids. These are carcinogenic compounds; therefore, nitrous acid test is not applied for secondary amines by the students. Tertiary aliphatic amines do not react with nitrous acid, but they form a soluble salt.

24 Tertiary aromatic amines react with nitrous acid to form the orange-colored hydrochloride salt of the C-nitrosoamine. Treating the solution with base liberates the blue or green C- nitrosoamine. Procedure : Nitrous acid is prepared instantaneously by the reaction of sodium nitrite and hydrochloric acid : In a test tube dissolve 0.5 ml or 0.5 g of the amine in a mixture of 1.5 ml of concentrated hydrochloric acid and 2.5 ml of water, and cool the solution to 0 C in a beaker of ice. In another test tube dissolve 0.5 g of sodium nitrite in 2.5 ml of water, and add this solution drop wise, with shaking to the cold solution of the amine hydrochloride. Move 2 ml of the final solution to another test tube, warm gently, and examine for evolution of gas.

25 Results : The observation of rapid bubbling or foaming as the aqueous sodium nitrite solution is added at 0 C indicates the presence of a primary aliphatic amine. The evolution of gas (bubbling) upon warming to room temperature indicates that the amine is a primary aromatic amine, and the solution should be subjected to the coupling reaction (test 3). If a pale yellow oil (heavier than water) or low-melting solid, which is the N-nitrosoamine, is formed with no evolution of gas, the original amine is a secondary amine. If a dark-orange solution or an orange crystalline solid is formed, which is the hydrochloride salt of the C- nitrosoamine, the amine is tertiary aromatic. Treating 2 ml of this solution with few drops of 10% sodium hydroxide or sodium carbonate solution produces the bright-green or -blue nitrosoamine base. If only solubilization of the amine is obtained with no other results, the amine is tertiary aliphatic. 3. Coupling reaction (a test for primary aromatic amines). Procedure : Dissolve 0.1 g of 2-naphthol in a mixture of 2 ml of 10% sodium hydroxide solution and 5 ml distilled water. Add 2 ml of the cold diazonium solution and observe the result. The formation of a red- orange dye (red precipitate in case of phenol) with evolution of gas only upon warming indicates that the compound is a primary aromatic amine.

26 4. Carbon disulfide reagent test (for secondary aliphatic amines). Procedure : In a test tube dissolve 50 mg (1-2 drops) of the amine in 5 ml distilled water (or 1-2 drops of concentrated hydrochloric acid if necessary). In another test tube mix o.5-1 ml of concentrated ammonia solution with 1 ml of nickel chloride in carbon disulfide reagent (NiCl 2 /CS 2 ). Add ml from the first test tube to the second one. A definite precipitation indicates that the unknown is a secondary amine. A slight turbidity is an indication of a trace of a secondary amine as an impurity. 5. Lignin test (for primary and secondary aromatic amines). This test depends on the action of lignin in the newsprint paper. Procedure : Dissolve mg of the amine in a few drops of ethanol and moisten a small area of newsprint paper with this solution. Place 2 drops of 6 N hydrochloric acid on the moistened spot. The immediate develop of yellow or orange colour is a positive test for a primary or secondary aromatic amine.

27 Experiment No.4 Identification Of Alkyl And Aryl Halides Physical properties : All alkyl halides and chlorobenzene are colourless liquids when pure except iodoform, CHI 3, which is a yellow crystalline solid with a characteristic odour. Methyl iodide, ethyl iodide and bromide, chloroform, and carbon tetrachloride have sweetish odours. Benzyl chloride has a sharp irritating odour and is lachrymatory. Chlorobenzene possesses aromatic odour. Alkyl and aryl halides (R-X, Ar-X) have boiling points higher than the parent hydrocarbon because of the heavier molecular weight. Accordingly, for a given compound, iodides have the higher boiling point than bromides and chlorides. In spite of their polarity alkyl halides are insoluble in water due to their inability to form hydrogen bonds. They are soluble in most organic solvents. Iodo-, bromo-, and polychloro- compounds are denser than water.

28 Chemical reactions : 1. Reaction with alcoholic silver nitrate. Alcoholic silver nitrate reagent is useful in classifying halogen compounds. Many halogen containing compounds react with silver nitrate to give an insoluble silver halide (AgX), and the rate of this reaction indicates the degree of reactivity of the halogen atom in the compound. Besides, the identity of the halogen can sometimes be determined from the colour of the silver halide produced; silver chloride is white (turns to purple on exposure to light), silver bromide is pale yellow, and silver iodide is yellow. These should, of course, be consistent with results from elemental analysis (sodium fusion for detection of halogens). It is obvious that this reaction follows S N 1 mechanism. Generally the reactivity of alkyl halides towards this reagent is: R 3 CX > R 2 CHX > RCH 2 X

29 Procedure : Add one drop or a couple of crystals of the unknown to 2 ml of 2% ethanolic silver nitrate solution. If no immediate reaction is observed, stand for 5 minutes at room temperature and observe the result. If no reaction takes place, warm the mixture in water bath for 30 seconds and observe any change. If there is any precipitate (AgX) add several drops of 1 M nitric acid solution to it; silver halides are insoluble in this acid. tert- chlorides, methyl and ethyl iodides, and ethyl bromide give fast result at room temperature whereas pri- and secchlorides, and benzyl chloride give result only on warming. Chlorobenzene, chloroform, iodoform and carbon tetrachloride don't give any positive result. 2. Sodium iodide in acetone test. This test, complementing the alcoholic silver nitrate test, is used to classify aliphatic chlorides and bromides as primary, secondary, or tertiary. This test depends on the fact that sodium chloride and sodium bromide are only very slightly soluble in acetone. The mechanism follows direct displacement (S N 2)process; therefore, the order of reactivity of simple halides is : primary > secondary > tertiary With sodium iodide, primary bromides give a precipitate of sodium bromide within 3 min at 25 C, whereas the chlorides give no precipitate and must be heated to 50 C in order to effect a reaction. Secondary and tertiary bromides react at 50 C, but the tertiary chlorides fail to react within the time specified. Tertiary chlorides will react if the test solutions are allowed to stand for a day or two.

30 These results are consistent with the following S N 2 process: Procedure : To 1 ml of the sodium iodide-acetone reagent in a test tube add two drops of the compound. If the compound is a solid, dissolve about 0.1 g in the smallest possible volume of acetone, and add the solution to the reagent. Shake the test tube, and allow the solution to stand at room temperature for 3 min. Note whether a precipitate is formed and also whether the solution turns reddish brown, because of the liberation of free iodine. If no change occurs at room temperature, place the test tube in water bath at 50 C.Excessive heating causes loss of acetone and precipitation of sodium iodide, which can lead to false-positive results. At the end of 6 min, cool to room temperature and note whether a reaction has occurred. Occasionally, a precipitate forms immediately after combination of the reagents; this represents a positive test only if the precipitate remains after the mixture is shaken and allowed to stand for 3 minutes.

31 3. Differentiation between alkyl and aryl halides (Formaldehyde- sulfuric acid test) With this test aryl halides (chlorobenzene) produce pink, red, or bluish red colour whereas alkyl halides produce yellow, amber, or brown colour. Procedure : This reagent is prepared at the time of use by adding 1 drop of formaldehyde to a test tube containing 1 ml concentrated sulfuric acid. In another test tube add 1 drop of the compound to be tested to 1 ml of hexane. From this solution take 1-2 drops and add them to 1 ml of the reagent. Shake well and observe the colour. 4. Special tests for chloroform a) Riemer- Tiemann reaction For procedure and chemical equations refer to "Identification of Phenols" experiment. Resorcinol results in a red colour with slight fluorescence in the aqueous layer while α- or β- naphthol results in a deep blue aqueous layer fading to green. b) Reduction of Fehling's reagent For preparation of Fehling's reagent and chemical equations refer to "Identification of Aldehydes and Ketones" experiment. Boil 1 ml of chloroform gently (water bath) with 3 ml of Fehling's reagent with constant shaking for 3-4 minutes. Reduction occurs and reddish cuprous oxide slightly separates.

32 Experiment No.5 Benzimidazole Introduction : Benzimidazole is a fused aromatic imidazole ring system where a benzene ring is fused to the 4 and 5 positions of an imidazole ring. Benzimidazole is also known as 1,3- benzodiazoles they possess both acidic and basic characteristics. The NH group present in benzimidazole is relatively strongly acidic and also weakly basic. Another characteristic of benzimidazole is that they have the capacity to form salts. Benzimidazole is a bicyclic heterocycle system consisting of two nitrogen atoms and fused phenyl ring shows wide range of biological activities.. Benzimidazole posses wide spectrum of biological activities including antibacterial, antifungal, antiviral, anti-inflammatory, anticonvulsant, antidepressant, antihypertensive, analgesic, and hypoglycemic properties. Benzimidazole can be synthesized using o- phenylenediamine and carboxylic acid. The reaction proceeds via the acyl derivatives which cyclizes under the influence of excess acid.

33 Procedure : A mixture of o-phenylenediamine (10 g ) with 90% formic acid (40 ml), placed in a 100 ml round bottom flask, heat at C on water bath for (1-2 hrs.) cool, dilute the reaction mixture with 20 ml cold water and add with stirring, dilute sodium hydroxide solution until the mixture is alkaline.collect the precipitated solid on bucchnner funnel and wash with cold water. Recrystallize from hot water and collect white crystals of benzimidazole m.p C. Calculation : O-Phenylene diamine Benzimidazole C 6 H 8 N 2 C 7 H 6 N g X X = gm theoretical wt.

34 Experiment No.6 Synthesis of 6- methyl 4- oxo- 1,2,3,4 tetrahydro thiopyrimidine Introduction : Pyrimidine is an aromatic heterocyclic organic compound similar to pyridine. One of the three diazines, (6-membered heterocyclics with two nitrogen atoms in the rings), it has the nitrogen atoms at positions 1 and 3 in the ring. The other diazines are pyrazine (nitrogen 1 and 4 ) and pyridazine (nitrogen 1 and 2). The pyrimidine ring system has wide occurrence in nature as substituted and ring fused compounds and derivatives, including the nucleotides, thiamine (vitamin B 1 ) and alloxane.

35 It is also found in many synthetic compounds such as barbiturates. Although pyrimidine derivatives such as uric acid and alloxane were known in the early 19 th century. The general pyrimidine synthesis involves the condensation of urea or urea derivatives with β-dicarbonyl compounds. The reaction of thiourea with ethyl acetoacetate yield 6- methyl4-oxo-1,2,3,4-tetrahydro-2-thiopyrimidine.

36 Procedure : To a mixture of thiourea (7.6 g ) and ethyl acetoacetate (14.8 ml ) in ethanol (10 ml) in a 100 ml. round bottomed flask,carefully add a solution of KOH ( 6.5 g ) in 4 ml water with stirring, and heat the mixture under reflux for 2 hours acidify the resulting crystalline mass by cautious addition of solution of concentrated HCl (20 ml) in water (10 ml), then cool and filter off the product. 6- methyl 4- oxo- 1,2,3,4- tetrahydro -2- thiopyrimidine is obtained as white crystals elting point C yield g (70-85 % ) Calculation : Ethyl acetoacetate 6-methyl 4-oxo-1,2,3,4-tetrahydro- 2-thiopyrimidine C 6 H 10 O 3 C 5 H 8 N 2 OS Wt = (14.8ml 1.02) g X X = g theoretical wt.