Of benzaldehydes

It is used for the preparation of benzaldehyde. For (his purpose it is usually heated with slaked lime and water under pressure. 

Nitrobenzene is a pale yellow liquid, having a b.p. 210 , and dy 1 20. It has an odour which is similar to that of almonds, and which is therefore often confused with that of benzaldehyde. Nitrobenzene is used chiefly for the preparation of aniline. 

Benzonitrile is a colourless liquid, having b.p. 190° and d, 1-02 it is almost insoluble in water, and has an odour resembling that of nitrobenzene and of benzaldehyde. 

Dissolve 0 3 ml. of glacial acetic acid in 2 ml. of water in a 25 ml. conical flask, and add 0 4 ml. (0 44 g.) of phenylhydrazine. Mix thoroughly to obtain a clear solution of phenylhydrazine acetate and then add 0 2 ml. (0 21 g.) of benzaldehyde. Cork the flask securely and shake the contents vigorously. A yellow crystalline mass of the hydrazone soon begins to separate. Allow to stand for 15 minutes, with occasional shaking, and then filter the solid product at the pump, wash first with very dilute acetic acid and then with water, and finally drain thoroughly. Recrystallise the material from rectified or methylated spirit, the benzaldehyde phenylhydrazone being thus obtained in fine colourless needles, m.p. 157 yield, 0 4 g. 

Place 5 ml. of benzaldehyde in a wide-necked stout-walled bottle of about 100 ml. capacity (a conical flask is too fragile for this purpose) and add 50 ml. of concentrated dy 0 880) ammonia solution. Cork the bottle securely, shake vigorously, and then allow to stand for 24 hours, by which time the layer of benzaldehyde at the bottom of the bottle will have been converted into a hard mass of hydrobenzamide. (If after 24 hours the crude hydrobenzamide is still syrupy, shake the mixture vigorously and allow to stand for another hour, when the conversion will be complete.) Break up the solid pellet with a strong spatula, filter at the pump, wash with water and drain thoroughly. Recrystallise from ethanol methylated spirit should not be used, as it contains sufficient water to cause partial hydrolysis back to benzaldehyde and ammonia. Hydrobenzamide is obtained as colourless crystals, m.p. 101° (and not 110° as frequently quoted) yield, 4 g. 

Mix I ml. of benzaldehyde and i ml. of aniline in a small evaporating-basin, place the latter on a boiling water-bath and stir the mixture gently with a glass rod. Globules of water soon appear on the oily layer. After about 20 minutes place the basin in ice-water, and stir the contents well, whereupon solidification should rapidly occur. (If the material does not solidify, replace the basin on the boiling water-bath for a further 10 minutes.) Break up the solid material in the basin, transfer to a conical flask, and recrystallise from rectified spirit. The benzylidene-aniline is obtained as colourless crystals, m.p, 52° yield, o-8 g. 

When an ethanolic solution containing both acetone and two equivalents of benzaldehyde is made alkaline with sodium hydroxide, rapid condensation occurs with the formation of dibenzal-acetone, or dibenzylidene-acetone. This... 

Dissolve I ml. of benzaldehyde and 0-4 ml. of pure acetone in 10 ml. of methylated spirit contained in a conical flask or widemouthed bottle of about 50 ml. capacity. Dilute 2 ml. of 10% aqueous sodium hydroxide solution with 8 ml. of water, and add this dilute alkali solution to the former solution. Shake the mixture vigorously in the securely corked flask for about 10 minutes (releasing the pressure from time to time if necessary) and then allow to stand for 30 minutes, with occasional shaking finally cool in ice-water for a few minutes. During the shaking, the dibenzal -acetone separates at first as a fine emulsion which then rapidly forms pale yellow crystals. Filter at the pump, wash well with water to eliminate traces of alkali, and then drain thoroughly. Recrystallise from hot methylated or rectified spirit. The dibenzal-acetone is obtained as pale yellow crystals, m.p. 112 yield, o 6 g. 

Note also that if another ester, of general formula R-COOCjHj, were used in place of benzaldehyde in the above reaction, a similar complex would be formed, and on acidification would give an unstable p-hydroxy-P-ethoxy ester, which would very readily lose ethanol with the formation of a 3-keto-ester. 

A 1500 ml. flask is fitted (preferably by means of a three-necked adaptor) with a rubber-sleeved or mercury-sealed stirrer (Fig. 20, p. 39), a reflux water-condenser, and a dropping-funnel cf. Fig. 23(c), p. 45, in which only a two-necked adaptor is shown or Fig. 23(G)). The dried zinc powder (20 g.) is placed in the flask, and a solution of 28 ml. of ethyl bromoacetate and 32 ml. of benzaldehyde in 40 ml. of dry benzene containing 5 ml. of dry ether is placed in the dropping-funnel. Approximately 10 ml. of this solution is run on to the zinc powder, and the mixture allowed to remain unstirred until (usually within a few minutes) a vigorous reaction occurs. (If no reaction occurs, warm the mixture on the water-bath until the reaction starts.) The stirrer is now started, and the rest of the solution allowed to run in drop-wise over a period of about 30 minutes so that the initial reaction is steadily maintained. The flask is then heated on a water-bath for 30 minutes with continuous stirring, and is then cooled in an ice-water bath. The well-stirred product is then hydrolysed by the addition of 120 ml. of 10% sulphuric acid. The mixture is transferred to a separating-funnel, the lower aqueous layer discarded, and the upper benzene layer then... 

Dinitrophenylhydrazones, To a few drops of formalin, add a few drops of 2,4-dinitrophenylhydrazine reagent A (p. 261) a yellow precipitate is produced in the cold. Acetaldehyde gives an orange-coloured precipitate. Dissolve a few drops of benzaldehyde or salicylal-dehyde in 2 ml. of methanol and then add a few drops of the reagent B an orange-coloured precipitate is obtained. In each case filter and recrystallise from ethanol. Take the m.p. (M.ps., p. 539-540.)... 

Oxidation to acids. Varm together in a small conical flask on a water-bath for lo minutes a mixture of 0 5 ml. of benzaldehyde or salicylaldehyde, 15 ml. of saturated KMn04 solution, and 0-5 g. of NajCOj. Then acidify with cone. HCl, and add 25% sodium sulphite solution until the precipitated manganese dioxide has redissolved. On cooling, benzoic or salicylic acid crystallises out. 

Bisulphite addition compound. Shake 1 ml. of benzaldehyde with about 0 5 ml. of saturated NaHSOj solution. The mixture becomes warm, and the white addition product separates (rapidly on cooling). 

Physical Properties. Nitrobenzene, C HjNOj pale yellow liquid, insoluble in and heavier than water, characteristic odour of bitter almonds, (similar to that of benzaldehyde and benzonitrile). /> Nitro toluene, C,H4(CH3)N02, usually pale yellow solid, insoluble in water, m-Dinitrobenzene, C8H4(N02)g, colourless solid when pure, but often pale yellow insoluble in water. 

The effect of superheated steam may be illustrated by reference to baizaldehyde, which boils at 178° at 760 mm. It distils with steam at 97-9° (Pj = 703-5 mm. and pg = 56-5 mm.) and the distillate contains 32-1 per cent, of benzaldehyde by weight. If one employs steam superheated to 133°, the vapour pressure of benzaldehyde (extrapolated from the boUing point - pressure curve) is 220 mm. hence pj = 540 (water), Pg = 220 (benzaldehyde), and... 

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. 

Evidence which suggests a possible mechanism of the reaction is provided by a study of the formation of benzaldehyde in poor yield from methylenebenzylamine benzaldehyde and ammonia (in equivalent amounts) and metliylbenzylamine are isolated ... 

The methylation of benzylamine (1) and of ammonia (2) are competitive processes by increasing the proportion of hexamine, the source of ammonia, the yield of benzaldehyde is increased and that of metliylbenzylamine is decreased. 

Place 45 g. (43 ml.) of benzal chloride (Section IV,22), 250 ml. of water and 75 g. of precipitated calcium carbonate (1) in a 500 ml. round-bottomed flask fltted with a reflux condenser, and heat the mixture for 4 hours in an oil bath maintained at 130°. It is advantageous to pass a current of carbon dioxide through the apparatus. Filter off the calcium salts, and distil the filtrate in steam (Fig. II, 40, 1) until no more oil passes over (2). Separate the benzaldehyde from the steam distillate by two extractions with small volumes of ether, distil off most of the ether on a water bath, and transfer the residual benzaldehyde to a wide-mouthed bottle or flask. Add excess of a concentrated solution of sodium bisulphite in portions with stirring or shaking stopper the vessel and shake vigorously until the odour of benzaldehyde can no longer be detected. Filter the paste of the benzaldehyde bisulphite compound at the pump... 

Benzoin condensation. Aromatic aldehydes when treated with an alkali cyanide, usually in aqueous solution, undergo condensation to the -hydroxyketone or benzoin. The best known example is the conversion of benzaldehyde to benzoin ... 

I) Sufficient alcohol is employed to dissolve the benzaldehyde and to retain the initially-formed benzalacetone in solution until it has had time to react with the second molecule of benzaldehyde. 

Stir a mixture of 2-4 g. of powdered hydrazine sulphate, 18 ml. of water and 2-4 ml. of concentrated aqueous ammonia (sp. gr. 0-88), and add 4-6 g. (4 4 ml.) of benzaldehyde (free from benzoic acid) dropwise, with stirring, over a period of 30-60 minutes. Stir the mixture for a further hour, collect the solid by suction filtration and wash it with water. RecrystalUse from 8 ml. of rectified spirit. The 3 ield of benzalazine (yellow needles), m.p. 92-93°, is 3-6 g. 

It is important to mix the mandelonitrile with hydrochloric acid immediately it has been separated from the water. Standing results in rapid conversion to the acetal of benzaldehyde and mandelonitrile C(H,CH[OCH(CN)C H,] and/or the iso-nitrile the yield of mandelic acid will, in consequence, be reduced. 

Azlactone of a-acetylaminocinnamic acid. Warm a mixture of 29 g. of acetylglycine, 39-5 g. (37 -5 ml.) of redistilled benzaldehyde (Section IV,115), 15 g. of anhydrous sodium acetate and 67 g. (62 ml.) of acetic anhydride (95 per cent.) in a 500 ml. conical flask (equipped with a reflux condenser) on a water bath with occasional stirring until solution is complete (10-20 minutes). Boil the resulting solution for 1 hour, cool and leave in a refrigerator overnight. Stir the sohd mass of yellow crystals with 60 ml. of cold water, transfer to a Buchner funnel and wash well with cold water. (If the odour of benzaldehyde is stih apparent, wash with a little ether.) Recrystallise from carbon tetrachloride or from ethyl acetate-hght petroleum. The yield of azlactone, m.p. 150°, is 35 g. 

Atophan (or cihchophen) may be prepared by condensing equimolecular proportions of benzaldehyde, aniline and pyruvic acid in alcoholic solution ... 

Strangely enough, cyanide ion is also involved in one special reaction giving an a-hydroxy-ketone. Can you show how the adduct A of benzaldehyde and cyanide ion can give a stable carbanion ... 

This anion now reacts with another molecule of benzaldehyde to give eventually the a-hydroxy-ketone 141 A. Draw mechanisms for these steps ... 

METHOD 2 [89]--1M MDA or benzedrine and 1M benzaldehyde is dissolved in 95% ethanol (Everclear), stirred, the solvent removed by distillation then the oil vacuum distilled to give 95% yellow oil which is a Schiff base intermediate. 1M of this intermediate, plus 1M iodomethane, is sealed in a pipe bomb that s dumped in boiling water for 5 hours giving an orangy-red heavy oil. The oil is taken up in methanol, 1/8 its volume of dH20 is added and the solution refluxed for 30 minutes. Next, an equal volume of water is added and the whole solution boiled openly until no more odor of benzaldehyde is detected (smells like almond extract). The solution is acidified with acetic acid, washed with ether (discard ether), the MDMA or meth freebase liberated with NaOH and extracted with ether to afford a yield of 90% for meth and 65% for MDMA. That s not a bad conversion but what s with having to use benzaldehyde (a List chemical) Strike wonders if another aldehyde can substitute. 

Styry] Dyes result from the condensation of benzaldehyde or p-dialkylaminobenzaldehyde with quaternary salts of 2-methylthiazole. either in acetic anhydride or in a solvent with a base as catalyst. 

TTie reaction of 2.4-dimethylselenazole with an excess of benzaldehyde gives a monostyryl derivative exclusively (12). Oxidation of 2,4-dimethyl-selenazole with selenium dioxide yields 4-methylselenazole (Scheme 30) (4). 

Under acidic conditions, a thiosemicarbazone intermediate (145) has been isolated, this can be cyclized in alcohol either into the corresponding 2-hydrazinothiazole (142) in the presence of benzaldehyde or into 1,3,4-thiadiazine (146) in the absence of benzaldehyde (Scheme 71) (375, 397, 408). 

By condensing carbon oxysulfide with o-aminOnitriles the corresponding 2-hydroxy-5-aminothiazoles can be obtained. In the presence of benzaldehyde or its substituted derivatives the reaction leads to 5-benzy-lideneaminothiazole derivatives (218) in good yields (Scheme 114 and Table 11.35) (393, 442). However, the reaction fails with or-amino acetonitrile (206), R = H (317). The 2-alkoxy analogs (220), R = Me, Et, Pr, Bu, vinyl, were similarly obtained from 219 and benzylideneamino acetonitrile (Scheme 115a) (393). 

Reactions were carried out by condensing the o-aminoacetonitrile with carbon oxysulfide in the presence of benzaldehyde or its substituted derivatives, in aicoho) as solvent. 

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