A-Hydroxy carboxylic acids

Fig. IV-20. Film pressure-area plots for cerebronic acid (a long-chain a-hydroxy carboxylic acid) and cholesterol (see insert) and for an equimolar mixture. At low pressures the r-a plot is close to that of the average (dashed line), an unanticipated kink then appears, and finally, the horizontal portion probably represents ejection of the cholesterol. (From Ref. 239.)...

Take two test-tubes A and B in A place about 5 ml. of neutralised tartaric acid solution and in B place 5 ml. of distilled water. To each solution add 3-4 drops of ferric chloride solution. Place a piece of white paper under the tubes, look down their length and note that A is definitely yellow compared with the control tube B. This yellow colour is given by a-hydroxy-carboxylic-acids, lactic acid, tartaric acid, citric acid. [Pg.333]

Nitrile groups m cyanohydrins are hydrolyzed under conditions similar to those of alkyl cyanides Cyanohydrin formation followed by hydrolysis provides a route to the preparation of a hydroxy carboxylic acids... [Pg.809]

These derivatives are prepared to protect a-hydroxy carboxylic acids they are cleaved by acidic hydrolysis of the acetal structure (HCl, DMF, 50°, 7 h, 71% yield), or basic hydrolysis of the lactone. ... [Pg.267]

Rearrangement of 1,2-diketones to give a-hydroxy carboxylic acids... [Pg.35]

Diketones 1 can be converted into the salt of an a-hydroxy carboxylic acid upon treatment with alkali hydroxide after acidic workup the free a-hydroxy carboxylic acid 2 is obtained. A well-known example is the rearrangement of benzil (R, R = phenyl) into benzilic acid (2-hydroxy-2,2-diphenyl acetic acid). The substituents should not bear hydrogens a to the carbonyl group, in order to avoid competitive reactions, e.g. the aldol reaction. [Pg.35]

The a-bromo or a-chloro carboxylic acids 2 are versatile intermediates for further synthetic transformations. For example they can be converted into a-hydroxy carboxylic acids by reaction with water by reaction with cyanide a-cyanocarboxylic acids 7 are obtained, which can be further converted to... [Pg.160]

The carbocations generated by non-Kolbe electrolysis can rearrange by alkyl, phenyl or oxygen migration. The migratory aptitudes of different alkyl groups have been studied in the rearrangement of a-hydroxy carboxylic acids (Eq. 34) [323]. [Pg.133]

Dutton reported on the synthesis of an e-caprolactam analog of an anthelmintic cyclic peptide. The a-hydroxy-e-caprolactam 44 was generated in an ex chiral pool synthesis staring from malic acid. The a-hydroxy carboxylic acid unit was protected as a dioxolanone in 43. The protective group served simultaneously as the reactive function during cyclization lactam 44 formation succeeded by ring opening of the dioxolanone 43 by the nucleophilic attack of the amino function, Eq. (8) [14]. [Pg.134]

Making use of the same reaction principle, disubstituted ketenes 66 have been reacted with aldehydes 80 to form p-lactones 81 [100], with diazo-compounds 82 to form 1,2-diazetidin-3-ones 83 [101] and with nitroso-compounds 84 to form 1,2-oxazetidin-3-ones 85 as precursors of a-hydroxy carboxylic acids (Fig. 42) [102],... [Pg.168]

The nitroaldol reaction or Henry reaction is a powerful and highly versatile carbon-carbon bond-forming reaction, allowing a plethora of key molecular frameworks, such as p-hydroxynitroalkanes, 1,2-amino alcohols or a-hydroxy carboxylic acids to be synthesised in a straightforward manner. Therefore, the development of practical catalytic asymmetric versions of this reaction is still largely desirable. The first catalytic asymmetric nitroaldol reaction was reported in 1992, " but despite its long history, relatively few chiral ligands have... [Pg.316]

Photolysis of 8-1 gives an isomeric compound 8-2 in 83% yield. Alkaline hydrolysis of 8-2 affords a hydroxy carboxylic acid, 8-3, C25H3204. Treatment of 8-2 with silica gel in hexane yields 8-4, C24H2802. 8-4 is converted by NaI04-KMn04 to a mixture of 8-5 and 8-6. What are the structures of 8-2, 8-3, and 8-4 ... [Pg.609]

Groger, H. (2001) Enzymatic routes to enantiomerically pure aromatic a-hydroxy carboxylic acids a further example for the diversity of biocatalysis. Advanced Synthesis and Catalysis, 343, 547-558. [Pg.193]

D-a-Hydroxy carboxylic acids.1 These optically active acids can be prepared by a Sn2 reaction between the t-butyl esters of L-2-halo carboxylic acids and cesium p-nitrobenzoate, which proceeds with complete inversion. [Pg.78]

Periodate oxidative cleavage of a-hydroxy carboxylic acids, RCHOHC02H... [Pg.451]

Osprian, 1., Fechter, M.H. and Griengl, H., Biocatal3ftic hydrolysis of cyanohydrins an efficient approach to enantiopure a-hydroxy carboxylic acids. J. Mol. Catal. B Enzymatic, 2003,24-25, 89-98. [Pg.114]

The nitroaldol (Henry) reaction constitutes a powerful C-C bond-forming process in organic chemistry, providing efficient access to valuable functionalized organic compounds such as 1,2-amino-alcohols, a-hydroxy-carboxylic acids and 3-hydroxy-nitroalkanes [215, 216]. [Pg.499]

A new stereocenter is formed when a synthon 143 with umpoled carbonyl reactivity (d reactivity) is introduced into aldehydes or imines. The enantioselective variant of this type of reaction was a longstanding problem in asymmetric synthesis. The very large majority of a-hetero-snbstitnted carbanions which serve as eqnivalents for synthons like 142 and 143 lead to racemic products with aldehydes or imines. However, enantiomerically pnre acylions and a-hydroxy carboxylic acids or aldehydes (144 and ent-144, respectively) as well as a-amino acids and aldehydes (145 and ent-145) are accessible either by nsing chiral d reagents or by reacting the components in the presence of chiral additives (Scheme 18). [Pg.877]

Various combinations of reactant(s) and process conditions are potentially available to synthesize polyesters [Fakirov, 2002 Goodman, 1988], Polyesters can be produced by direct esterification of a diacid with a diol (Eq. 2-120) or self-condensation of a hydroxy carboxylic acid (Eq. 2-119). Since polyesterification, like many step polymerizations, is an equilibrium reaction, water must be continuously removed to achieve high conversions and high molecular weights. Control of the reaction temperature is important to minimize side reactions such as dehydration of the diol to form diethylene glycol... [Pg.92]

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