Benzaldehyde benzoin

Benzaldehyde, benzoin, cinnamic aldehyde, salicylic aldehyde, furfurol, and quinone, under the influence of the discharge, absorb nitrogen more or less rapidly. 

Benzaldehyde, benzoin and benzhydrol derivatives are obtained in the reaction of FefCO), with LiPh, followed by hydrolysis. The scheme in Egs. (f) and (g) is assumed to explain the observed products, starting with the formation of the anionic lithiated benzoyl derivative, which upon hydrolysis gives benzaldehyde. 

Oxime lassen sich mit Hydrazin bei Anwesenheit von Raney-Nickel als Katalysator zu Aminen reduzieren1. Die Ausbeuten sind vergleichbar mit denen, die bei der Reduktion mit Lithiumalanat erzielt werden. Die Oxime von Heptanal, Benzaldehyd, Benzoin und Campher werden nicht reduziert, in einigen Fallen wird ein Nickelkomplex, in einigen Fallen ein Pyrazolin-Derivat gebildet. 

Many aromatic aldehydes (having the -CHO group joined directly to the benzene ring) undergo polymerisation when heated with a solution of potassium cyanide in aqueous ethanol. Thus benzaldehyde gives benzoin, a compound of double function, since it contains both a secondary alcoholic and a ketonic... 

C6H5CH(0H)CN I HCOCgHi - C6H5CH(OH)COC H, - HCN unchanged benzaldehyde, giving benzoin and regenerating the hydrogen cyanide... 

Add 5 g. of powdered potassium cyanide to a mixture of 20 ml. of water and 50 ml. of ethanol contained in a 200 ml. conical flask, and then add 25 mi. (26 g.) of freshly distilled benzaldehyde. Fit the flask with a reflux water-condenser, and boil the mixture gently on a water-bath for 30 minutes, a clear solution being rapidly obtained. Then pour the solution into a beaker and cool the benzoin separates as a crystalline mass... 

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 ... 

In a 500 ml. round-bottomed flask place 65 ml. of rectified spirit, 50 g. (47 5 ml.) of pure benzaldehyde (1) and a solution of 5 g. of sodium cyanide (96-98 per cent.) CAUTION) in 50 ml, of water. Attach a reflux condenser (preferably of the double surface type) and boil the mixture gently for half an hour (2). Cool the contents of the flask (preferably in an ice bath). Filter the crude benzoin, wash it with cold water, drain well (3) and dry. The yield of crude benzoin, which is white or pale yellow in colour, is 45 g. 

ALkah metal cyanides catalyze the condensation of benzaldehyde to form benzoin. 

Benzoin, [119-53-9] 2-hydroxy-2-phenylacetophenone, CgH CH(OH)COCgH (mp, 133—137°C bp, 343—344°C at 101.3 kPa), is formed by the self-condensation of benzaldehyde in the presence of potassium cyanide. It is used on a small scale as a polymerization catalyst in polyester resin manufacture. 

Triphenylethylene has been prepared by the reaction of phenylmagnesium bromide with benzyl benzoate, with desoxy-benzoin, or with ethyl pheaniylacetate, and by the reaction of diphenylketene-quinoline with benzaldehyde. The above procedure is an adaptation of that described by Hell and Wiegandt. ... 

The mixture of benzaldehyde, potassium cyanide and alcohol is heated on the water-bath with an upright condenser for about half an hour. On cooling the liquid, the benzoin separates out as a mass of small colourless crystals, which are filtered and u ashed with a little alcohol. Yield, about 20 grams. A portion of the substance may be purified by recrystalhsation from spirit. 

Benzoin -As a small cjnantity of potassium cyanide is (apable of converting a large quantity of benzaldehyde into bciv/oin, the action of the cyanide has been explained as follows. The potassium cyanide first reacts with the aldehyde and forms a cyanhydnn, which then condenses with another molecule of aldehyde, hydrogen cyanide being finally eliminated (Lapwortbj,... 

Active carbonyl compounds such as benzaldehyde attack the electron-rich double bond in DTDAFs to give a dipolar adduct, which immediately undergoes dissociation with formation of two molecules of 146 (64BSF2857 67LA155).Tlie existence of by-products such as benzoin led to the synthetic application of thiazolium salts in the acyloin condensation. For example, replacement of the classic cyanide ion by 3-benzyl-4-methyl-5(/3-hydroxyethyl) thiazolium salts allowed the benzoin-type condensation to take place in nonaqueous solvents (76AGE639) (Scheme 57). 

The triazole 76, which is more accurately portrayed as the nucleophilic carbene structure 76a, acts as a formyl anion equivalent by reaction with alkyl halides and subsequent reductive cleavage to give aldehydes as shown (75TL1889). The benzoin reaction may be considered as resulting in the net addition of a benzoyl anion to a benzaldehyde, and the chiral triazolium salt 77 has been reported to be an efficient asymmetric catalyst for this, giving the products (/ )-ArCH(OH)COAr, in up to 86% e.e. (96HCA1217). In the closely related intramolecular Stetter reaction e.e.s of up to 74% were obtained (96HCA1899). 

The first asymmetric benzoin reactions were reported by Sheehan and Hannemann nsing chiral thiazolinm salt pre-catalyst 100 of unknown absolute configuration [40], Low yields and enantioselectivities were obtained, and although a wide range of thiazolium salt pre-catalysts have since been studied, of which 101-105 are representative, the enantioselectivities obtained for the condensation of benzaldehyde using thiazolium pre-catalysts are generally poor (Scheme 12.19) [41],... 

R)-Benzoins and (/ )-2-hydroxypropiophcnonc derivatives are formed on a preparative scale by benzaldehyde lyase (BAL)-catalyzed C-C bond formation from aromatic aldehydes and acetaldehyde in aqueous buffer/DMSO solution with remarkable ease in high chemical yield and high optical purity (Eq. 8.112).303 Less-stable mixed benzoins were also generated via reductive coupling of benzoyl cyanide and carbonyl compounds by aqueous titanium(III) ions.304... 

This method has an analogy in the well known acyloin condensation, a reaction which takes place between two molecules of an aromatic aldehyde in a solution containing an alkali cyanide. Thus for example, benzaldehyde gives rise to benzoin, a compound in which the enediolic system, —C(OH)=C(OH)—, exists mainly in the ketonic form —CO—CHOH—. If a hydroxy aldehyde like D-glucose (X) is allowed to... 

The procedure described is essentially that of Ballard and Dehn.1 Stilbene has also been prepared by reduction of desoxy-benzoin,20 benzaldehyde,23 and benzil 2o-2c by dehydrogenation of ethyl benzene,30 toluene,30- 33- 3, and bibenzyl 33-3alkaline reduction of phenylnitromethane,40 phenylnitroacetonitrile,40 and desoxybenzoin 43 by distillation of benzyl sulfone,50 benzyl sulfide,60-63 calcium cinnamate,5 cinnamic acid,5d phenyl cinna-mate,6e-6/ and diphenyl fumarate ie by dehydrohalogenation of a,a -dichlorobibenzyl60 and benzyl chloride 63 by dehalogenation of a,a,c/,a -tetrachlorobibenzyl70 and benzal chloride 73 by the coupling of cinnamic acid and phenyldiazonium chloride 8 by de-... 

The synthesis of 3-H-oxazol-2-ones was described by Nam et al. [69]. The substituted benzoin 89 was formed from the coupling of 3,4,5-trimethoxy-benzaldehyde 18 with 3-nitro-4-methoxybenzaldehyde, Scheme 22. Reaction with PMB-isocyanate and subsequent cyclization gave the protected oxazolone derivative 90. The PMB group was removed by reflux in TFA and reduction of the nitro-group was performed using Zn to give the combretoxazolone-aniline 91. 

Freshly distilled benzaldehyde (10 g.) is mixed with 25 c.c. of alcohol and a solution of 2 g. of potassium cyanide in 5 c.c. of water. The mixture is boiled on the water bath under reflux for one hour. Then the product is allowed to cool slowly, and the crystals which form, after being separated by filtration and washed with a little alcohol, are dried on the water bath. In order to obtain some quite pure benzoin a small sample of the crude product is recrystallised from a little alcohol. Melting point 134°. Yield about 90 per cent of the theoretical. 

The benzoin condensation of benzaldehyde in the presence of potassium cyanide has been studied by Akabori et al. (1976). Under liquid-liquid... 

Tetra-n-butylammonium cyanide is a better catalyst for benzoin condensation reactions than is sodium cyanide, and >70% yields are obtained under mild conditions [63, 64] tetra-ethylammonium cyanide is less effective. Polymer-supported ammonium catalysts have also been used to promote the benzoin reaction and, although yields are only moderate (40-60%), the convenience of removal of the catalyst is an advantage. Use of chiral ammonium groups produces an enantiomeric excess of chiral products from the condensation of benzaldehyde, but furfural tends to produce a racemate [65]. 

Colorless to white needles, scales, or powder with a faint benzoin or benzaldehyde-like odor. Shaw et al. (1970) reported a taste threshold in water of 85 ppm. 

The known property of diorganyl tellurides of reducing metallic salts, applied to tita-nium(IV) chloride, generates a titanium(III) species which is a useful reagent for some selective reductions. By this method benzaldehyde is reduced to dihydrobenzoin, and benzyl to benzoin, and successively to desoxybenzoin. ... 

It oxidizes thiophenol to diphenyl disulphide, hydroquinone to p-benzoquinone, benzoin to benzyl, benzylic alcohols to the corresponding carbonyl compounds and cleaves hydrobenzoin to benzaldehyde. 

The benzoin reaction dates back to 1832 when Wohler and Liebig reported that cyanide catalyzes the formation of benzoin 6 from benzaldehyde 5, a seminal example in which the normal mode of polarity of a functional group was reversed (Eq. 1) [26], This reversal of polarity, subsequently termed Umpolung [27], effectively changes an electrophilic aldehyde into a nucleophilic acyl anion equivalent. 

In 1903, Lapworth described his findings of the action of potassium cyanide on benzaldehyde [28], He postulated that cyanide adds to benzaldehyde to form V, followed by proton transfer of the a-labile hyd rogen, forming intermediate VI which is now referred to as an acyl anion equivalent. Addition to another molecule of benzaldehyde occurs to form VII (Scheme 1). The unstable cyanohydrin of benzoin VII then collapses to form benzoin and potassium cyanide. Additionally, Lapworth tested the reversibility of the addition of cyanide to benzaldehyde by first forming hydroxybenzyl cyanide (protonated variant of V) and subjecting it to benzaldehyde and base, in which benzoin was recovered. 

Miiller and co-workers have developed an enantioselective enzymatic crossbenzoin reaction (Table 2) [43, 44], This is the first example of an enantioselective cross-benzoin reaction and takes advantage of the donor-acceptor concept. This transformation is catalyzed by thiamin diphosphate (ThDP) 23 in the presence of benzaldehyde lyase (BAL) or benzoylformate decarboxylase (BFD). Under these enzymatic reaction conditions the donor aldehyde 24 is the one that forms the acyl anion equivalent and subsequently attacks the acceptor aldehyde 25 to provide a variety of a-hydroxyketones 26 in good yield and excellent enantiomeric excesses without contamination of the other cross-benzoin products 27. The authors chose 2-chlorobenzaldehyde 25 as the acceptor because of its inability to form a homodimer under enzymatic reaction conditions. 

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