M-benzaldehydes

Because the carbon atom attached to the ring is positively polarized a carbonyl group behaves m much the same way as a trifluoromethyl group and destabilizes all the cyclo hexadienyl cation intermediates m electrophilic aromatic substitution reactions Attack at any nng position m benzaldehyde is slower than attack m benzene The intermediates for ortho and para substitution are particularly unstable because each has a resonance structure m which there is a positive charge on the carbon that bears the electron withdrawing substituent The intermediate for meta substitution avoids this unfavorable juxtaposition of positive charges is not as unstable and gives rise to most of the product... 

In situ formation of an oxaziridine is possible using a reagent combination of chloramine-M, benzaldehyde, and benzyltriethylammonium chloride <2000JA4039>. While the oxidation of /ra t-alkenes generates /ra t-oxiranes, the corresponding reaction of air-alkenes produces /ra t-oxiranes as major products. 

Figure 9.40 Fluorinations of m-benzaldehydes using a nine-channel microreactor, where —X is — NO2, —CN, CF3, or —CHO functional group. Source Reprinted with permission from Ref [121]. Copyright (2009) American Chemical Society.

Demir AS, e enoglu 6, Diinkelmann P, Muller M. Benzaldehyde lyase-catalyzed enantioselective carboligation of aromatic aldehydes with mono- and dimethoxy acetaldehyde. Org. Lett. 2003 5 2047-2050. 

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. 

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. 

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.)... 

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. 

Benzaldehyde reacts with hydroxylamine in the presence of excess of sodium hydroxide to 3deld an oxime of low m.p. (a- or. gjM-benzaldoxime) which is stable to alkah, but is rapidly rearranged by acids to give an isomeric oxime of higha m.p. ( 3- or < i/r-benzaldoxlme) ... 

In a 500 ml. wide-mouthed reagent bottle place a cold solution of 25 g. of sodium hydroxide in 250 ml. of water and 200 ml. of alcohol (1) equip the bottle with a mechanical stirrer and surround it with a bath of water. Maintain the temperature of the solution at 20-25°, stir vigorously and add one-half of a previously prepared mixture of 26-5 g. (25 -5 ml.) of purebenzaldehyde (Section IV,115) and 7 -3 g. (9-3 ml.) of A.R. acetone. A flocculent precipitate forms in 2-3 minutes. After 15 minutes add the remainder of the benzaldehyde - acetone mixture. Continue the stirring for a further 30 minutes. Filter at the pump and wash with cold water to eliminate the alkali as completely as possible. Dry the solid at room temperature upon filter paper to constant weight 27 g. of crude dibenzalacetone, m.p. 105-107°, are obtained. Recrystallise from hot ethyl acetate (2-5 ml. per gram) or from hot rectified spirit. The recovery of pure dibenzalacetone, m.p. 112°, is about 80 per cent. 

Place 10 ml. of pure benzaldehyde (Section IV,115) and 100 ml. of concentrated aininonia solution (sp. gr. 0-88) in a 250 ml. wide-mouthed reagent bottle. Cork the bottle securely, shake vigorously for 10 minutes and allow to stand with occasional shaking for 24 hours. By this time the benzaldehyde should be converted into a hard mass of hydrobenz-amide. Break up the solid mass with a spatula or a thick glass rod, filter with suction, wash with water, and drain thoroughly. RecrystalUse from absolute alcohol (or absolute methylated spirit). The yield of hydrobenzamide (colourless crystals), m.p. 101°, is 7 g. It is easily hydrolysed by cold dilute acids. 

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. 

Place 35 ml. of a M solution of aluminium tsopropoxide or 7 g. of solid aluminium tsopropoxide, 450 ml. of dry isopropyl alcohol and 21 g. of purified benzaldehyde (Section IV,115) in a 1 litre round-bottomed flask. Fit a short reflux condenser (no water in the cooling jacket) or better a Hahn condenser (2) (containing a 1 cm. layer of ethyl alcohol in the iimer tube) to the flask and arrange for slow distillation from a water bath at the rate of 3-6 drops per minute. Continue the heating until a negative test for acetone is obtained after 5 minutes of total reflux (6-9 hours) if the volume of the mixture falls below 200 ml. during the reduction, add more isopropyl alcohol. Remove the reflux or Hahn condenser and distil off (Fig. II, 13, 3) most of the isopropyl alcohol under atmospheric pressure from a suitable oil bath. Hydrolyse the... 

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. 

Azlactone of a-benzoylaminocinnamic acid. Place a mi.xture of 27 g. (26 ml.) of redistilled benzaldehyde, 45 g. of Mppuric acid (Section IV,54), 77 g. (71-5) ml. of acetic anhydride and 20-5 g. of anhydrous sodium acetate in a 500 ml. conical flask and heat on an electric hot plate with constant shaking. As soon as the mixture has liquefied completely, transfer the flask to a water bath and heat for 2 hours. Then add 100 ml. of alcohol slowly to the contents of the flask, allow the mixture to stand overnight, filter the crystalline product with suction, wash with two 25 ml. portions of ice-cold alcohol and then wash with two 25 ml. portions of boiling water dry at 100°. The yield of almost pure azlactone, m.p. 165-166°, is 40 g. Recrystallisation from benzene raises the m.p. to 167-168°. 

Atophan. In a 1 litre round-bottomed flask, equipped with a reflux condenser, place 25 g. (24 ml.) of purified benzaldehyde (Section IV,115), 22 g. of freshly-distilled P3 ruvic acid and 200 ml. of absolute ethyl alcohol. Heat the mixture to tlie boiling point on a water bath and add slowly, with frequent shaking, a solution of 23 g. (22 -5 ml.) of pure aniline in 100 ml. of absolute ethyl alcohol. The addition usually occupies about 1 hour. Reflux the mixture on a water bath for 3 hours, and allow to stand overnight. Filter off the crude atophan (1) at the pump and wash the crystals with a little ether. Recrystallise from ethyl alcohol (about 20 ml. per gram). The yield of pure 2-phenvlquinoUne-4-carboxvUc acid, m.p. 210°, is 30 g. 

The reactivity of 2-methylselenazole toward carbonyl compounds is the same as its thiazoie homolog. Reaction of 2,4-dimethylselenazole with benzaldehyde in the presence of anhydrous zinc chloride as catalyst gives 4-methyl-2-styrylselenazoie [m.p. 74-75 C (19)] (Scheme 43). 

The behavior of aromatic aldehydes is typical Nitration of benzaldehyde takes place sev eral thousand times more slowly than that of benzene and yields m mtrobenzaldehyde as the major product... 

To understand the effect of a carbonyl group attached directly to the ring consider Its polarization The electrons m the carbon-oxygen double bond are drawn toward oxy gen and away from carbon leaving the carbon attached to the nng with a partial posi tive charge Using benzaldehyde as an example... 

A few cyanohydrins and ethers of cyanohydrins occur naturally One species of millipede stores benzaldehyde cyanohydrin along with an enzyme that catalyzes its cleavage to benzaldehyde and hydrogen cyanide m separate compartments above its legs When attacked the insect ejects a mixture of the cyanohydrin and the enzyme repelling the invader by spraying it with hydrogen cyanide... 

The mechanism for formation of benzaldehyde diethyl acetal which proceeds m two stages is presented m Figure 17 9 The first stage (steps 1-3) involves formation of a hemiacetal m the second stage (steps 4-7) the hemiacetal is converted to the acetal Nucleophilic addition to the carbonyl group characterizes the first stage carbocation chemistry the second The key carbocation intermediate is stabilized by electron release from oxygen... 

Figure 17 10 presents the mechanism for the reaction between benzaldehyde and methylamine given m the first example The first two steps lead to the carbmolamme the last three show the dehydration of the carbmolamme to the imine Step 4 the key... 

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