The analysis and identification of unknown organic compounds constitutes a very important aspect of experimental organic chemistry. There is no definite set procedure that can be generally applied to organic qualitative analysis. Various books have different approaches, but a systematic approach based on the scheme given below will give good results. Students should, however, consult the laboratory manual and Textbook of Practical Organic Chemistry, A.I. Vogel (4th Edition). Practical Notes Before outlining the general scheme, one or two points of practical importance should be noted. Quantities of substance for tests. For most tests about 0.1 g solid or 0.1 - 0.2 mL (2 - 3 drops) of liquid material (NOT MORE) should be used. Reagents likely to be met within organic analysis are on the reagent shelves. Students are advised to develop a general knowledge of the physical characteristics of common organic compounds. If in doubt about the expected result of a test between a certain compound and a reagent, carry out a trial test with a known compound and compare with the unknown. Quantities of substance derivatives. Students have wasted much time and material in the past by taking too large a quantity of substance for preparation of a derivative. In general, 0.5 - 1 g (or 0.5 - 1 mL) of substance gives the most satisfactory results. If a practical book instructs one to use larger quantities (3 - 4 g or more), the quantities should be scaled down to 1 g or 1 mL of the unknown substance and corresponding quantities of reagents should be used. General Scheme of Analysis Preliminary Tests Note physical characteristics - solid, liquid, colour and odour. Perform an ignition test (heat small amount on metal spatula) to determine whether the compound is aliphatic or aromatic (i.e. luminous flame - aliphatic; sooty flame - aromatic). Physical Constants Determine the boiling point or melting point. Distillation is recommended in the case of liquids (see Appendix 3). It serves the dual purpose of determining the b.p., as well as purification of the liquid for subsequent tests. Analysis for elements present At C10 level, the elements present will be told to you, but read up the method. Solubility tests The solubility of the unknown in the following reagents provides very useful information. In general, about 3 mL of the solvent is used with 0.1 g or 0.2 mL (2 - 3 drops) of the substance. The class of compound may be indicated from the following table: REAGENT AND TEST CLASS GROUP OF COMPOUNDS Soluble in cold or hot water. (If the unknown is soluble do NOT perform solubility tests below) Neutral, acidic or basic. (Test with litmus or universal indicator paper) Lower members of series. Neutral, e.g. alcohols; Acidic, e.g. acids, phenols; Basic, e.g. amines Soluble in dil. HCl Basic Most amines (except III amines with only aromatic groups Soluble in dil. NaOH Acidic Most acids, most phenols. Soluble in NaHCO3 Strongly acidic Most carboxylic acids. Insoluble in water, acid and alkali Neutral Hydrocarbons, nitrohydro-carbons, alkyl or aryl halides, esters and ethers. Higher molecular weight alcohols, aldehydes and ketones Group Classification Tests From the previous tests it is often possible to deduce the functional groups present in the unknown compound. Consult i.r. spectra when available. Individual tests are then performed to identify and confirm the functional groups present. Note Students are strongly advised against carrying out unnecessary tests, since not only are they a waste of time but also increase the possibility of error. Thus it is pointless to first test for alcohol or ketone in a basic compound containing nitrogen! Instead tests for amines, etc. should be done on such a compound. A systematic approach cannot be overemphasised in group classification tests to avoid confusion and error. Consultation of Literature Once the functional group has been identified, reference is made to tables in a book on organic analysis, for assessing possibilities and for the preparation of suitable solid derivatives. It should be noted that whilst two substances with the same functional group may sometimes have very similar b.p. or m.p., solid derivatives can usually be chosen from the literature, with m.p. differences of about 10 (or more), which distinguish between the two possibilities. Example: COMPOUND B.P. DERIVATIVES (M.P.) 2,4-DNPH SEMICARBAZONE Diethyl ketone 102 156 139 Methyl n-propyl ketone 102 144 112 Preparation of derivatives The final characterisation of the unknown is made by the preparation of suitable solid derivatives. The derivative should be carefully selected and its m.p. should preferably be between 90 - 150 for ease of crystallisation and m.p. determination. Preparation of one derivative should be attempted. The derivative should be purified by recrystallisation, dried and the m.p. determined. Derivatives should be submitted correctly labelled for assessment together with the record. Recording of Results The results should be recorded in a systematic manner. Results should be recorded in the practical book at the time (not written up afterwards). A record should be made of every test carried out, no matter whether a NEGATIVE RESULT HAS BEEN OBTAINED . Test, observation and inference should be given. At the conclusion of the analysis a brief summary of results should be included, giving the name, b.p. or m.p., and formula of the analysed compound. Qualitative Analysis for Elements (for reference only) In organic compounds the elements commonly occurring along with carbon and hydrogen, are oxygen, nitrogen, sulphur, chlorine, bromine and iodine. The detection of these elements depends upon converting them to water-soluble ionic compounds and the application of specific tests. Lassaigne's Sodium Fusion Test C, H, O, N, S, X NaX NaCN -> Na2S NaCNS Procedure Place a piece of clean sodium metal, about the size of a pea into a fusion tube. Add a little of the compound (50 mg or 2 - 3 drops).* Heat the tube gently at first, allowing any distillate formed to drop back onto the molten sodium. When charring begins, heat the bottom of the tube to dull redness for about three minutes and finally plunge the tube, while still hot, into a clean dish containing cold distilled water (6 mL) and cover immediately with a clean wire gauze.** Caution *For liquids it is better to first melt the sodium add the liquid drop by drop. ** The tube shatters, and any residual sodium metal reacts with water. Stir the mixture, boil for 1 - 2 minutes, on a tripod and filter hot through a fluted paper. The 'fusion' filtrate which should be clear and colourless, is used for the SPECIFIC TESTS DESCRIBED BELOW: To a portion (2 mL) of the 'fusion' filtrate add 0.2 g of powdered ferrous sulphate crystals. Boil the mixture for a half a minute, cool and acidify by adding dilute sulphuric acid dropwise. Formation of a bluish-green precipitate (Prussian blue) or a blue solution indicates that the original substance contains nitrogen. If no precipitate appears, allow to stand for 15 minutes, filter and inspect filter paper. SULPHUR (SULPHIDE) To the cold 'fusion' filtrate (1 mL) add a few drops of cold, freshly prepared, dilute solution of sodium nitroprusside. The latter may be prepared by adding a small crystal of the solid to 2 mL of water. Production of a rich purple colour indicates that the original substance contains sulphur. This test is very sensitive. Only strong positive results are significant. HALOGENS (HALIDES) Acidify a portion (1 mL) of the 'fusion' filtrate with 2N nitric acid, and if nitrogen and/or sulphur are present, boil for 1 - 2 minutes.* Cool and add aqueous silver nitrate (1 mL), compare with a blank. Formation of a heavy, white or yellow precipitate of silver halide indicates halogen. If a positive result is obtained: acidify the remaining portion of the 'fusion' filtrate with dilute sulphuric acid, boil and cool. Add carbon tetrachloride (1 mL) and a few drops of freshly prepared chlorine water. Shake the mixture. If the carbon tetrachloride layer remains colourless - indicates chlorine. If the carbon tetrachloride layer is brown - indicates bromine. If the carbon tetrachloride layer is violet - indicates iodine. *If nitrogen and/or sulphur are also present, the addition of silver nitrate to the acidified 'fusion' solution will precipitate silver cyanide and/or silver sulphide in addition to the silver halides. The removal of hydrogen cyanide and/or hydrogen sulphide is effected by boiling the 'fusion' solution. GROUP CLASSIFICATION TESTS Some functional group tests are listed below. Students should refer to a practical text book for details, and further information, e.g. Vogel. Tests for unsaturation Cold dilute potassium permanganate solution. Solution of bromine in carbon tetrachloride. Tests for compounds containing nitrogen Amines Nitrous acid. Confirmatory tests. Compounds which give amines or ammonia on acid or alkaline hydrolysis: Amides, substituted amides, anilides, nitriles. Compounds which give amines on reduction: Nitro, nitroso, azo, hydrazo, nitriles. Tests for compounds containing C, H and possibly oxygen Carboxylic acids \(\ce{Na2CO3}\) or \(\ce{NaHCO3}\) solution liberate carbon dioxide. Phenols Sodium hydroxide solution (soluble). Insoluble in and no \(\ce{CO2}\) from \(\ce{NaHCO3}\) (except when electron attracting groups present, e.g. 2,4-dinitrophenol). Ferric chloride solution. Bromine water. Aldehydes and Ketones 2,4-dinitrophenylhydrazine (as Brady's reagent) for \(\ce{C=O}\). Iodoform test for \(\ce{CH3CO-}\). Aldehydes only (reducing properties) Fehling's solution. Tollen's reagent (ammoniacal \(\ce{AgNO3}\) solution). Jones reagent. Alcohols Lucas' reagent to distinguish I, II and III alcohols. Jones reagent. Metallic sodium (use dry liquid and dry tube). Sugars Molisch's test. Esters Hydroxamic acid test. Hydrolysis. Write up of the identification of an unknown organic compound Date...................................... Compound containing C, H (N, Hal, S) Physical characteristics ...................... (solid, liquid, gas, colour, odour, etc.) Ignition test .............................. (aromatic or aliphatic) Physical constant ........................ (boiling point or melting point) Solubility tests (in tabular form) Group classification tests (in tabular form) Test Observation Inference From the above tests and observations the given compound is probably a .........................(acid, phenol, aldehyde, etc.) Consultation of literature (Possibilities) M.P. of derivative (a) (b) (c) Preparation of derivative (method of preparation) Observed m.p. of derivative Lit. m.p. of derivative Result Compound No. ........................ is ............................ (give formula) Tests for Functional Groups UNSATURATED COMPOUNDS Two common types of unsaturated compounds are alkenes and alkynes characterised by the carbon-carbon double and triple bond, respectively, as the functional group. The two common qualitative tests for unsaturation are the reactions of the compounds with (a) bromine in carbon tetrachloride and (b) potassium permanganate. 2% Bromine in carbon tetrachloride Dissolve 0.2 g (or 0.2 mL) of the compound in 2 mL of carbon tetrachloride or another suitable solvent and add the solution dropwise to 2 ml of 2% bromine solution in carbon tetrachloride and shake. e.g. Rapid disappearance of the bromine colour to give a colourless solution is a positive test for unsaturation. Note The reagent is potentially dangerous. Keep it off your skin and clothes; protect your eyes and nose. 2% Aqueous potassium permanganate Dissolve 0.2 g (or 0.2 mL) of the substance in 2 mL of water (acetone may also be used as solvent). Add the potassium permanganate solution dropwise and observe the result. e.g. For a blank determination, count the number of drops added to 2 mL of acetone before the colour persists. A significant difference in the number of drops required in the two cases is a positive test for unsaturation. COMPOUNDS CONTAINING NITROGEN Amines Reaction with nitrous acid Dissolve the amine (0.5 mL) in concentrated acid (2.0 mL) and water (3 mL) and cool the solution to 0 - 5 in an ice-bath for 5 minutes. Add a cold solution (ice-bath) of sodium nitrite (0.5 g) in water (2.0 mL) from a dropper, with swirling of the test tube, still keeping the mixture in the ice-bath. AMINE REACTION I aliphatic N2 evolved. RNH2 + HNO2 -> ROH + N2 + H2O __________________________________________________________________ I aromatic Diazonium salt is formed. ArNH2 + HNO2 -> ArN=N+ Add the cold diazonium solution and with swirling to a cold solution of 2-naphthol (0.2 g) in 5% NaOH solution (2 mL). An orange-red azo dye is formed. __________________________________________________________________ II aliphatic and Yellow oily nitrosamines are generally formed. II aromatic R2NH + HNO2 -> R2N-NO __________________________________________________________________ III aliphatic No visible reaction. __________________________________________________________________ III aromatic Dialkylanilines yield green solid p-nitroso compounds (if p-position unsubstituted). __________________________________________________________________ Reaction with benzenesulphonyl chloride Benzenesulphonyl chloride reacts with primary and secondary but not with tertiary amines to yield substituted sulphonamides. e.g. \(\ce{C6H5SO2Cl + H-NHR + NaOH -> C6H5SO2NHR + NaCl + H2O}\) \(\ce{C6H5SO2Cl + H-NR2 + NaOH -> C6H5SO2NR2 + NaCl + H2O}\) The substituted sulphonamide formed from a primary amine dissolves in the alkali medium whilst that produced from a secondary amine is insoluble in alkali. Place 0.5 mL (or 0.5 g) of the compound, 15 - 10 mL of 5% NaOH and 1 mL of benzenesulphonyl chloride in a test tube, stopper the tube and shake until the odour of the sulphonyl chloride has disappeared. The solution must be kept alkaline (if no reaction has occurred, the substance is probably a tertiary amine). If a precipitate appears in the alkaline solution, dilute with about 10 mL of water and shake; if the precipitate does not dissolve, a secondary amine is indicated. If there is no precipitate, acidify it cautiously to congo red with concentrated hydrochloric acid (added dropwise): a precipitate is indicative of a primary amine. Amides \(\ce{R-CO-NH2}\) Simple primary amides can be decomposed by boiling with alkali and thereby evolving ammonia. e.g. CH3-CO-NH2 + NaOH -> CH3-CO2- Na+ + NH3 ­ Boil 0.5 g of the compound with 5 mL of 10% sodium hydroxide solution and observe whether ammonia is evolved. COMPOUNDS CONTAINING C, H AND POSSIBLY OXYGEN Carboxylic acids - test with 5% aq. \(\ce{NaHCO3}\) R-CO2H + NaHCO3 -> R-CO2- Na+ + CO2 ­ + H2O Sodium hydrogen carbonate reacts with carboxylic acids to give the sodium salt of the acid and liberates carbon dioxide. If the acid is insoluble in water and the reaction is sluggish dissolve the acid in methanol and add carefully to a saturated sodium hydrogen carbonate solution, when a vigorous effervescence will be observed. Phenols [Soluble in \(\ce{NaOH}\) and produce no \(\ce{CO2}\) from \(\ce{NaHCO3}\)] Bromine water Phenols are generally highly reactive towards electrophilic reagents and are readily brominated by bromine water. e.g. Dissolve or suspend about 0.05 g of the compound in 2 mL of dilute hydrochloric acid and add bromine water dropwise until the bromine colour remains. A white precipitate of the bromophenol may form. Solid bromophenol derivatives can be used for the confirmation of the structure of a phenol (cf the preparation of derivatives). Ferric chloride test Most phenols react with iron (III) chloride to form coloured complexes. The colours vary - red, purple, blue or green - depending on various factors, e.g. the phenolic compound used, the solvent, concentration. Since some phenols do not give colours, a negative test must not be taken as significant without supporting information. Dissolve 0.05 g of the compound in 2 mL water (or a mixture of water and ethanol if the compound is not water-soluble) and add an aqueous solution of ferric chloride dropwise. Observe any colour changes which may occur. Aldehydes and ketones 2,4-Dinitrophenylhydrazine (as Brady's reagent) A test for the carbonyl group (\(\ce{C=O}\)) in aldehydes and ketones. 2,4-Dinitrophenylhydrazine gives sparingly soluble yellow or red 2,4-dinitrophenylhydrazones with aldehydes and ketones. Add 3 mL of the reagent to 2 drops of the compound in a test tube and shake. If no precipitate forms immediately, warm and allow to stand for 5 - 10 minutes. A crystalline precipitate indicates the presence of a carbonyl compound. The bench reagent is very dilute and is intended for qualitative tests only and should not be used in the preparation of a derivative for identification purposes. (b) Iodoform test for \(\ce{CH3CO-}\) Dissolve 0.1 g (or 5 drops) of the compound in 2 mL of water; if it is insoluble in water add sufficient dioxan to produce a homogeneous solution. Add 2 mL of 5% NaOH solution and then introduce the potassium iodide - iodine reagent dropwise with shaking until a definite dark colour of iodine persists. Allow to stand for 2 - 3 minutes; if no iodoform separates at room temperature, warm the test tube in a beaker of water at 60 . Add a few more drops of the iodine reagent if the faint iodine colour disappears. Continue the addition of the reagent until a dark colour is not discharged after 2 minutes heating at 60 . Remove the excess of iodine by the addition of a few drops of dilute sodium hydroxide solution with shaking, dilute with an equal volume of water, and allow to stand for 10 minutes. The test is positive if a yellow precipitate of iodoform is deposited. Filter off the yellow precipitate, dry upon pads of filter paper and determine the m.p. Iodoform melts at 120 (it can be recrystallised from methanol- water). The reaction is given by acetaldehyde and simple methyl ketones. Alcohols containing the \(\ce{CH3CHROH}\) group will be oxidised under the reaction conditions and also give a positive test. Aldehydes only (reducing properties). Fehling's solution Aldehydes reduce Fehling's solution to yellow or red copper (I) oxide. Preparation of the reagent: Mix equal volumes of Fehling's solution solution I (aqueous alkaline potassium tartrate) and Fehling's solution II (copper sulphate solution). Add 2 drops (or 0.05 g) of the compound and 2 - 3 drops of the reagent and heat on a boiling water bath for 3 - 4 minutes. The test is positive for aliphatic aldehydes, but is often indecisive for aromatic aldehydes where Jones' Reagent is often useful (see 5). Tollen's reagent (Ammonical silver nitrate solution) Aldehydes are readily oxidised to carboxylic acids and will reduce Tollen's reagent to produce a silver mirror on the inside of a clean test tube. FIRST clean up a test tube with a little hot nitric acid (fume cupboard) and rinse with distilled water. Preparation of the reagent: To 1 mL of silver nitrate solution add a few drops of sodium hydroxide. Then add dilute ammonium hydroxide dropwise until the precipitate just dissolves. Add 2 - 3 drops of the compound in methanol to 2 - 3 mL of Tollen's solution contained in a very clean test tube. If no reaction takes place in the cold, warm gently in a water bath. CAUTION: After the test, pour the contents of the test tube into the sink and wash the test tube with dilute nitric acid. Any silver fulminate present, which is highly explosive when dry, will be destroyed. Jones Reagent (See section under alcohols). Alcohols: The tests for the hydroxyl group not only detect the presence of the group, but may also indicate whether it is primary, secondary or tertiary. Jones Reagent (CrO 3 -H 2 SO 4 in H 2 O) This reagent distinguishes primary and secondary alcohols from tertiary alcohols; the test is based on the much greater resistance to oxidation of tertiary alcohols compared to the other two types. Aldehydes also give a positive test. Place 1 mL of acetone in a test tube and dissolve one drop of a liquid or ca 10 mg of a solid alcohol or aldehyde in it. Add one drop of the reagent to the acetone solution and shake the tube to mix the contents. Primary and secondary alcohols react within two seconds as indicated by the disappearance of the orange colour of the reagent and the formation of a green or blue-green precipitate or emulsion. Tertiary alcohols do not react even after 3 minutes. (I) RCH2OH -> RCHO -> RCO2H (II) R2CHOH -> R2C=O (III) R3COH -> no visible reaction. Lucas' Reagent [ZnCl 2 - conc. HCl] This reagent converts alcohols into the corresponding alkyl chlorides. Zinc chloride (a Lewis acid) increases the reactivity of alcohols towards acid. The test depends on the rate of reaction of primary, secondary, and tertiary alcohols with the reagent at room temperature. (I) RCH2OH -> no reaction at room temperature. (II) R2CHOH -> R2CHCl + H2O (1 hour or maybe longer) (III) R3COH -> R3CCl + H2O (immediately) To 1 mL of the alcohol in a small test tube add 6 mL of Lucas' reagent at room temperature. Close the tube with a cork, shake and allow to stand. Primary alcohols - the aqueous phase remains clear (except allyl alcohol - droplets after 7 minutes). Secondary alcohols - very slow reaction (~ 1 hour or maybe longer) when droplets of alkyl chloride may be seen. Tertiary alcohols - very fast reaction and droplets of the alkyl chloride formed almost immediately. Sugars, Carbohydrates Molisch's Test This is a general test for carbohydrates. Dissolve 20 - 30 mg of the compound in 2 mL water and add 0.5 mL of the reagent (a 20% solution of 2-naphthol in ethanol). Pour 2 mL of concentrated sulphuric acid from a dropper carefully down the side of the tube so that the acid forms a layer beneath the aqueous solution without mixing with it. A red colouration, changing to dark purple forms at the interface. Carry out a second test on a blank solution. Esters Hydroxamic acid test R-CO-OR' + H2N-OH -> R-CO-NH-OH + R'-OH Esters react with hydroxylamine in the presence of sodium hydroxide to form the sodium salt of the corresponding hydroxamic acid. On acidification and addition of ferric chloride the magenta-coloured iron (III) complex of the hydroxamic acid is formed. It is always advisable to ensure that an unknown compound does not give a colour with iron (III) chloride before carrying out the hydroxamic acid test. Procedure for hydroxamic acid test Ferric chloride test Dissolve a drop or a few small crystals of the compound in 1 mL of 95% ethanol (rectified spirit) and add 1 mL of M hydrochloric acid. Note the colour produced when 1 drop of 5% iron (III) chloride is added to the solution. If a pronounced violet, blue, red or orange colour is produced, the hydroxamic acid test described below is NOT APPLICABLE. Hydroxamic acid test Mix 1 drop or several small crystals (ca 0.05 g) of the compound with 1 mL of 0.5 M hydroxylamine hydrochloride in 95% ethanol and add 0.2 mL of 6 M aqueous sodium hydroxide. Heat the mixture to boiling and after the solution has cooled slightly add 2 mL of M hydrochloric acid. If the solution is cloudy, add 2 mL of 95% ethanol. Observe the colour produced when 1 drop of 5% iron (III) chloride solution is added. If the resulting colour does not persist, continue to add the reagent dropwise until the observed colour pervades the entire solution. Usually only 1 drop of the iron (III) chloride solution is necessary. Compare the colour with that produced in test (a). A positive test will be a distinct burgundy or magenta colour as compared with the yellow colour observed when the original compound is tested with iron (III) chloride solution in the presence of acid. It is often advisable to conduct in parallel the test with, say, ethyl acetate, to ensure that the conditions for this test are correct. The Preparation of Derivatives of Organic Compounds The preliminary examination and group classification tests indicate the particular class (functional group) to which an unknown organic compound may belong. Further characterisation and identification depends on the selection and preparation of a suitable solid derivative and accurate determination of its melting point (best, between 90 - 150 ). The following table lists some of the classes of organic compounds and a selection of derivatives that may be prepared to characterise them. Check with the tables of melting points in Vogel which derivatives are most suitable for the characterisation of your particular compound. 0 1 CLASS OF COMPOUND DERIVATIVES 1. ALCOHOLS 3,5-dinitrobenzoate 2. PHENOLS benzoate, acetate, bromo-derivative 3. ALDEHYDES AND KETONES semicarbazone, 2,4-dinitrophenyl-hydrazone, oxime 4. ACIDS anilide, amide, p-toluidide. 5. AMINES benzoyl, acetyl and sulphonamide derivatives METHODS FOR THE PREPARATION OF DERIVATIVES ALCOHOLS 3,5-Dinitrobenzoates 3,5-Dinitrobenzoyl chloride is usually partially hydrolysed and should be prepared in the pure state by heating gently a mixture of 3,5-dinitrobenzoic acid (1 g) and phosphorus pentachloride (1.5 g) in a dry test tube, until it liquifies (5 min).* The liquid is poured on a dry watch glass and allowed to solidify. The phosphoryl chlorides are removed by pressing the solid with a spatula on a wad of filter paper. The residual acid chloride is suitable for immediate use in the preparation of the derivatives. *Work under fume hood. Fumes are irritating to the eyes and nose. The 3,5-dinitrobenzoyl chloride is mixed with the alcohol (0.5 - 1 mL) in a loosely corked dry test tube and heated on a steam bath for about 10 min. Secondary and tertiary alcohols require up to 30 min. On cooling add 10 mL sodium hydrogen carbonate solution, stir until the ester crystallises out, and filter at the pump. Wash with a little carbonate solution, water and suck dry. Recrystallise from the minimum hot ethanol or light petroleum. Cool slowly to avoid the formation of oily droplets of your ester. PHENOLS Benzoates (Schötten-Baumann method). To the phenol (0.5 g) is added 5% sodium hydroxide (10 mL) in a well-corked boiling tube or a small conical flask. Benzoyl chloride (2 mL) is added in small quantities at a time, and the mixture shaken vigorously with occasional cooling under the tap or in ice-water. After 15 min the solid benzoate separates out: the solution should be alkaline at the end of the reaction; if not alkaline, or if the product is oily, add a solid pellet of sodium hydroxide and shake again. Collect the benzoate, wash thoroughly with cold water, and recrystallise from alcohol or light petroleum. Acetates Acetates of many simple phenols are liquids; however, this is a suitable derivative for polyhydric and substituted phenols. The phenol (0.5 g) is dissolved in 10% sodium hydroxide solution and an equal quantity of crushed ice is added, followed by acetic anhydride (2 mL). The mixture is vigorously shaken in a stoppered test tube until the acetate separates. The product is filtered and recrystallised from alcohol. Bromo derivatives The phenol (0.3 g) is suspended in dilute hydrochloric (10 mL) and bromine water added dropwise until no more decolourisation occurs. The bromo derivative which precipitates out is filtered off and recrystallised from alcohol. ALDEHYDES AND KETONES Semicarbazones Dissolve semicarbazide hydrochloride (1 g) and sodium acetate (1.5 g) in water (8 - 10 mL), add the aldehyde or ketone (0.3 mL) and shake. Shake the mixture for a few minutes and then cool in ice-water. Filter off the crystals, wash with a little cold water and recrystallise from methanol or ethanol. 2,4-Dinitrophenylhydrazones Suspend 0.25 g of 2,4-dinitrophenylhydrazine in 5 mL of methanol and add 0.5 mL of concentrated sulphuric acid cautiously. Filter the warm solution and add a solution of 0.2 g of the carbonyl compound in 1 mL of methanol. Recrystallise the derivative from methanol, ethanol or ethyl acetate. Oximes Hydroxylamine hydrochloride (0.5 g) is dissolved in water (2 mL). 10% sodium hydroxide (2 mL) and the carbonyl compound (0.2 - 0.3 g) dissolved in alcohol (1 - 2 mL) are added, the mixture warmed on a steam bath for 10 min and then cooled in ice. Crystallisation is induced by scratching the sides of the test tube with a glass rod. The oximes may be crystallised from alcohol. ACIDS Amides, anilides and p-toluidides The acid (0.5 g) is refluxed with thionyl chloride (2 - 3 mL) in a fume cupboard for about 30 mins.* It is advisable to place a plug of cotton wool in the top of the reflux condenser to exclude moisture. The condenser is removed and the excess of thionyl chloride is distilled off (b.p. 78 ). The acid chloride thus produced is treated with concentrated ammonia solution (5 mL) or aniline (0.5 - 1 mL) or p-toluidine (0.5 - 1 g), when the solid derivative separates out. It is collected and recrystallised from alcohol adding decolourising charcoal if found necessary. *Alternately use PCl 5 to form the acid chloride. AMINES Acetyl derivatives (acetamides) Reflux gently in a small dry flask under a dry condenser the amine (1 g) with acetic anhydride (3 mL) for 15 min. Cool the reaction mixture and pour into 20 mL cold water. Boil to decompose the excess acetic anhydride. Cool and filter by suction the insoluble derivative. Recrystallise from ethanol. Benzoyl derivatives (benzamides) Suspend 1 g of the amine in 20 mL of 5% aqueous sodium hydroxide in a well-corked flask, and add 2 mL benzoyl chloride (fume hood!), about 0.5 mL at a time, with constant shaking. Shake vigorously for 5 - 10 min until the odour of the benzoyl chloride has disappeared. Ensure that the mixture remains alkaline. Filter off the solid derivative, wash with a little cold water and recrystallise from ethanol. Benzenesulphonamides To 1 g of the amine in 20 mL of 5% sodium hydroxide solution in a well-corked flask add 1 mL benzenesulphonyl chloride (fume hood!). Shake the mixture until the odour of the sulphonyl chloride disappears. Check that the solution is alkaline. Acidify if necessary to obtain the precipitated derivative. Concentrated hydrochloric acid added dropwise should be used. Filter the product, wash with a little cold water and suck dry. Recrystallise from ethanol.