Alcohols from

When alcohols undergo dehydration reactions, alkenes are generated. There is a chance of rearrangement of the carbocation intermediates to form more stable carbocation intermediates, whenever possible, resulting in the formation of more than one type of alkenes. The mechanisms of such rearrangements are discussed in Chapter 21. 

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R NHa + C.HjNCO = RNH CO NHC,Hj Traces of water will contaminate the product with diphenylurea (p. 336) if the solution is boiled hence the need for anhydrous conditions. i-Naphthylisocyanate reacts more slowly with water, and the i-naphthyl-urea derivative can often be obtained using a cold aqueous solution of an aliphatic amine it is particularly necessary in such cases to purify the product by recrystallisation from, or extraction with, boiling petroleum, leaving behind any insoluble di i-naphthylurea. Note that the amine must also be free from alcohols (p. 335) and phenols (p. 337). 

Pure chloroform has b.p. 61°/760 mm. The solvent, when free from alcohol, should be kept in the dark in order to avoid the photochemical formation of phosgene. It must not be dried with sodium as an explosion may occur. 

The ureas are less soluble than the corresponding urethanes, but their separation is not always easy. For this reason the urethanes are generally prepared from alcohols which are insoluble in water and can therefore be easily obtained in the anhydrous condition. 

Heat a little pseudo-saccharin chloride with excess of the anhydrous alcohol in a test-tube until hydrogen chloride is no longer evolved. Recrystallise from alcohol or other organic solvent. 

Three general methods are available for the preparation of iodides from alcohols —... 

Owing to the corrosive action of bromine upon corks j-jg 7, l. and rubber stoppers, ground glass joints are recommended in this preparation. The apparatus, depicted in Fig. Ill, 37, 1, is particularly convenient for the preparation of bromides from alcohols. A double surface condenser is fitted into D and a round-bottomed flask is fitted on to the ground glass joint at C R is a three-way stopcock f which permits the removal of the contents of A without disconnecting the apparatus. For preparations of moderate size, A has a capacity of 60 or 100 ml. and a 250 or 500 ml. flask is attached at C. 

A special apparatus (Fig. Ill, 40,1) renders the preparation of iodides from alcohols a very simple operation. The special features of the apparatus are —(i) a wide bored (3-4 mm.) stopcock A which considerably reduces the danger of crystallisation in the bore of the tap of the iodine from the hot alcoholic solution (ii) a reservoir B for the solid iodine and possessing a capacity sufficiently large to hold all the alkyl iodide produced (iii) a wide tube C which permits the alcohol vapour fix)m the flask D to pass rapidly into the reservoir B, thus ensuring that the iodine is dissolved by alcohol which is almost at the boiling point. An improved apparatus is shown in Fig. Ill, 40, 2, a and b here a... 

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

Suspend 0 25 g. of 2 4-dinitrophenylhydrazine in 5 ml. of methanol and add 0-4 0-5 ml. of concentrated sulphuric acid cautiously. FUter the warm solution and add a solution of 0 1-0-2 g. of the carbonyl compound in a small volume of methanol or of ether. If no sohd separate within 10 minutes, dUute the solution carefuUy with 2N sulphuric acid. CoUect the solid by suction filtration and wash it with a little methanol. RecrystaUise the derivative from alcohol, dUute alcohol, alcohol with ethyl acetate or chloroform or acetone, acetic acid, dioxan, nitromethane, nitrobenzene or xylene. 

For water insoluble aldehydes or ketones, the following alternative procedure may be used. Reflux a mixture of 0-6 g. of the aldehyde or ketone, 0 5 g. of hydroxylamine hydrochloride, 5 ml. of ethanol and 0 5 ml. of pyridine on a water bath for 15-60 minutes. Remove the alcohol either by distillation (water bath) or by evaporation of the hot solution in a stream of air (water pump). Add 5 ml. of water to the cooled residue, cool in an ice bath and stir until the oxime crystallises Filter off the solid, wash it with a little water and dry. Recrystallise from alcohol (95 per cent, or more dilute), benzene, or benzene - light petroleum (b.p. 60-80°). 

Dissolve 0 5 g. of the primary amine and 0-5 g. of pure phthaUc anhydride in 5 ml. of glacial acetic acid and reflux for 20-30 minutes. (If the amine salt is used, add 1 g. of sodium acetate.) The N-substituted phthaUmide separates out on cooling. Recrystallise it from alcohol or from glacial acetic acid. 

Heat 0-25 g. of the compound with 3 ml. of alcohol, add 0-25 g. of p-nitrophenylhydrazine, and heat the suspension until the reaction appears complete. The p-nitrophenylhydrazone soon separates. Filter, preferably after standing overnight, wash with a little cold alcohol, and then recrystallise from alcohol. 

Preparation of 2 4-dinitrophenyl-sulphides. Dissolve about 0-5 g. (or 0 005 mol) of the mercaptan in 10-15 ml, of rectified spirit (or in the minimum volume necessary for solution warming is permissible) and add 2 ml. of 10 per cent, sodium hydroxide solution. Mix the resulting sodium mercaptide solution with a solution of 1 g. of 2 4-dinitrochlorobenzene in 5 ml. of rectified spirit. Reaction may occur immediately with precipitation of the thioether. In any case reflux the mixture for 10 minutes on a water bath in order to ensure the completeness of the reaction. Filter the hot solution rapidly allow the solution to cool when the sulphide will crystaUise out. RecrystaUise from alcohol. 

Preparation of the sulphones. Dissolve the 2 4-dinitrophenyl-sulphide in the minimum volume of warm glacial acetic acid and add 3 per cent, potassium permanganate solution with shaking as fast as decolourisation occurs. Use a 50 per cent, excess of potassium permanganate if the sulphide tends to precipitate, add more acetic acid. Just decolourise the solution with sulphur dioxide (or with sodium bisulphite or alcohol) and add 2-3 volumes of crushed ice. Filter off the sulphone, dry, and recrystaUise from alcohol. 

Triphenylmethane dissolves in about one-third of its weight of warm benzene it crystallises with one molecule of benzene of crystallisation which is lost on exposure to air or heating on a water bath or by recr3 stallisation from alcohol. 

Picrates are usually prepared by mixing solutions of equivalent quantities of the two components in the minimum volume of rectified spirit and allowing to cool the derivative separates in a crystalline condition. It is filtered off, washed with a little ether, and pressed on a porous tUe. If the picrate is stable, it is recrystaUised from alcohol, ethyl acetate or ether. 

Diphenyl. Reflux a mixture of 1 g, of diphenyl, 2 ml. of glacial acetic acid and 0 -5 ml. of fuming nitric acid for 10 minutes. Pour into 20 ml. of cold water, filter oflF the precipitate, wash it with cold water imtil free from acid, and recrystallise from alcohol. The product is 4-nitrodiphenyl, m.p. 114°,... 

The nitrates should be evaporated to small bulk and the separated solid recrystallised twice from alcohol. 

Add 25 g. of finely-powdered, dry acetanilide to 25 ml. of glacial acetic acid contained in a 500 ml. beaker introduce into the well-stirred mixture 92 g. (50 ml.) of concentrated sulphuric acid. The mixture becomes warm and a clear solution results. Surround the beaker with a freezing mixture of ice and salt, and stir the solution mechanically. Support a separatory funnel, containing a cold mixture of 15 -5 g. (11 ml.) of concentrated nitric acid and 12 -5 g. (7 ml.) of concentrated sulphuric acid, over the beaker. When the temperature of the solution falls to 0-2°, run in the acid mixture gradually while the temperature is maintained below 10°. After all the mixed acid has been added, remove the beaker from the freezing mixture, and allow it to stand at room temperature for 1 hour. Pour the reaction mixture on to 250 g. of crushed ice (or into 500 ml. of cold water), whereby the crude nitroacetanilide is at once precipitated. Allow to stand for 15 minutes, filter with suction on a Buchner funnel, wash it thoroughly with cold water until free from acids (test the wash water), and drain well. Recrystallise the pale yellow product from alcohol or methylated spirit (see Section IV,12 for experimental details), filter at the pump, wash with a httle cold alcohol, and dry in the air upon filter paper. [The yellow o-nitroacetanihde remains in the filtrate.] The yield of p-nitroacetanihde, a colourless crystalline sohd of m.p. 214°, is 20 g. 

If the mixture is cooled in ice, most of the p-acetotoluidide separates out in a crj-stalline form. It may be recrystallised from alcohol. 

Dissolve 200 g. of sodium nitrite in 400 ml. of water in a 2-litre beaker provided with an efficient mechanical stirrer, and add 40 g. of copper powder (either the precipitated powder or copper bronze which has been washed with a little ether). Suspend the fluoborate in about 200 ml. of water and add it slowly to the well-stirred mixture. Add 4-5 ml. of ether from time to time to break the froth. The reaction is complete when all the diazonium compound has been added. Transfer the mixture to a large flask and steam distil until no more solid passes over (about 5 litres of distillate). Filter off" the crystalline solid in the steam distillate and dry upon filter paper in the air this o-dinitrobenzene (very pale yellow crystals) has m.p. 116° (t.c., is practically pure) and weighs 29 g. It may be recrystallised from alcohol the recrystallised solid melts at 116-5°. 

Frequently the recrystallized azobenzeno has m.p. 61°, which is unaffected by recrystallisation from alcohol. Upon distillation from a. 50 ml. distilling flask fitted with a short air condenser, the m.p. is raised to 67-5° and the recovery is about 90 per cent. one recrystallisation from diluted alcohol (as above) then gives perfectly pure azobenzene of m.p. 68-5°. 

To isolate the triphenylguanidine, dilute the residue in the flask with 50 ml. of water, add 2-3 g. of decolourising carbon, warm, and filter. Cool the solution in ice, and filter oflF the hydrochloride at the pump. Dissolve it in the minimum volume of hot water, render the solution alkaline with sodium hydroxide, and allow to cool. Filter off the free base (triphenylguanidine), and recrystallise it from alcohol it separates in colourless crystals, m.p. 144°, The yield is 3 g. 

Method 1. Treat 2 0 g. of the mixture of amines with 40 ml. of 10 per cent, sodium hydroxide solution and add 4 g. (3 ml.) of benzenesulphonyl chloi de (or 4 g. of p-toluenesulphonyl chloride) in small portions. Warm on a water bath to complete the reaction. Acidify the alkaline solution with dilute hydrochloric acid when the sulphonamides of the primary and secondary amines are precipitated. Filter off the solid and wash it with a little cold water the tertiary amine will be present in the filtrate. To convert any disulphOnamide that may have been formed from the primary amine into the sulphonamide, boil the solid under reflux with 2 0 g. of sodium dissolved in 40 ml. of absolute ethyl alcohol for 30 minutes. Dilute with a little water and distil off the alcohol filter off the precipitate of the sulphonamide of the secondary amine. Acidify the filtrate with dilute hydrochloric acid to precipitate the derivative of the primary amine. Recrystallise the respective derivatives from alcohol or from dilute alcohol, and identify them inter alia by a determination of the m.p. 

Method 2. Place a 3 0 g. sample of the mixture of amines in a flask, add 6g. (4-5 ml.) of benzenesulphonyl chloride (or 6 g. of p-toluenesulphonyl chloride) and 100 ml. of a 5 per cent, solution of sodium hydroxide. Stopper the flask and shake vigorously until the odour of the acid chloride has disappeared open the flask occasionally to release the pressure developed by the heat of the reaction. AUow the mixture to cool, and dissolve any insoluble material in 60-75 ml. of ether. If a solid insoluble in both the aqueous and ether layer appears at this point (it is probably the sparingly soluble salt of a primary amine, e.g., a long chain compound of the type CjH5(CH2) NHj), add 25 ml. of water and shake if it does not dissolve, filter it off. Separate the ether and aqueous layers. The ether layer will contain the unchanged tertiary amine and the sulphonamide of the secondary amine. Acidify the alkaline aqueous layer with dilute hydrochloric acid, filter off the sulphonamide of the primary amine, and recrystaUise it from dilute alcohol. Extract the ether layer with sufficient 5 per cent, hydrochloric acid to remove all the tertiary amine present. Evaporate the ether to obtain the sulphonamide of the secondary amine recrystaUise it from alcohol or dilute alcohol. FinaUy, render the hydrochloric acid extract alkaline by the addition of dilute sodium hydroxide solution, and isolate the tertiary amine. 

Suspend 1 g. (or 1 ml.) of the substance in 20 ml. of 5 per cent, sodium hydroxide solution in a well-corked boiling tube or small conical flask, and add 2 ml. of redistilled benzoyl chloride, ca. 0-5 ml. at a time, with constant shaking, and cooling in water (if necessary). Shake vigorously for 5-10 minutes until the odour of the benzoyl chloride has disappeared. Make sure that the mixture has an alkaline reaction. Filter oflF the solid benzoyl derivative, wash it with a little cold water, and recrystalHse it from alcohol or dilute alcohol. 

Treat 1 g. (1 ml.) of the amine with 4 mols of 10 per cent, sodium or potassium hydroxide solution (say, 20 ml,), and add 1 -5 mols (or 3 g. if the molecular weight is unknown) of benzenesulphonyl or p-toluenesulphonyl chloride in small portions with constant shaking. To remove the excess of acid chloride, either shake vigorously or warm gently. Acidify with dilute hydrochloric acid and filter off the sulphonamide. Recrystallise it from alcohol or dilute alcohol. 

If the presence of a disulphonyl derivative from a primary amine is suspected (e.., formation of a precipitate in alkaline solution even after dilution), reflux the precipitate, obtained after acidifyim , with a solution of I g. of sodium in 20 ml. of rectifled spirit for 15 minutes. Evaporate the alcohol, dilute with water, and filter if necessary acidify with dilute hydrochloric acid. Collect the sulphonyl derivative and recrystallise it from alcohol or dilute alcohol. 

Reflux a mixture of 1 g. (1 ml.) of the amine, 2-3 g. of benzenesulphonyl chloride and 6 ml. of pyridine for 30 minutes. Pour the reaction mixture into 10 ml. of cold water and stir until the product crystallises. Filter off the solid and recrystaUise it from alcohol or dilute alcohol. 

Heat the amine with one or two mols of redistilled benzaldehyde (according as to whether the base is a monamine or diamine) to 100° for 10 minutes if the molecular weight is unknown, use 1 g. of the base and 1 or 2 g. of benzaldehyde. Sometimes a solvent, such as alcohol (5 ml.) or acetic acid, may be used. Recrystallise from alcohol, dilute alcohol or benzene. 

In a 1 htre round bottomed flask equipped with a reflux condenser place a solution of 62 -5 g. of anhydroas sodium carbonate in 500 ml. of water and add 50 g. of commercial 2 4-dinitro-l-chlorobenzene. Reflux the mixture for 24 hours or until the oil passes into solution. Acidify the yellow solution with hj drochloric acid and, when cold, filter the crystaUine dinitrophenol which has separated. Dry the product upon filter paper in the air. The yield is 46 g. If the m.p, differs appreciably from 114°, recrystallisc from alcohol or from water. 

Dissolve 0 -5 g. of the phenol in 4-5 ml. of dry p ridine, add 1 - 3 g. of 3 5-dinitrobenzoyl chloride and reflux for 25-30 minutes. Pour the cold reaction mixture into 40 ml. of ca. 2N hydrochloric acid. Decant the supernatant aqueous hquid from the precipitated sohd or oil and stir it vigorously with about 10 ml. of N sodium carbonate solution. Filter off the sohd derivative and wash it with water. RecrystaUise from alcohol, dilute alcohol, benzene - acetone or benzene - light petroleum (b.p. 60-80 ),... 

Dissolve 0-5 g. of the phenol in 2 -5 ml. of pyridine, and add one equivalent of dlphenylcarbamyl chloride (or 0- 0-5 g. if the molecular weight is uncertain). Reflux the mixture for 30-60 minutes on a boiling water bath, and then pour into about 25 ml. of water. Filter the derivative, wash with a little sodium bicarbonate solution, and recrystallise from alcohol benzene, light petroleum (b.p. 60-80°) or carbon tetrachloride. 

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