Hell-Volhard-Zelinskii reaction

Palladium Reagents in Organic Syntheses, Academic Press, New York, 1985. [Pg.159]

Guzman-Perez, Angew. Chem. 1998, HO, 402 15 Angew. Chem. Int. Ed. Engl. 1998, 37, 388. [Pg.159]

By application of the Hell-Volhard-Zelinskii reaction,an a-hydrogen of a carboxylic acid 1 can be replaced by bromine or chlorine to give an a-bromo-or a-chlorocarboxylic acid 2 respectively. [Pg.159]

In the following the reaction is outlined for an a-bromination. The reaction mechanism involves formation of the corresponding acyl bromide 3 by reaction of carboxylic acid 1 with phosphorus tribromide PBr3. The acyl bromide 3 is in equilibrium with the enol derivative 4, which further reacts with bromine to give the a -bromoacyl bromide 5 [Pg.159]

The a -brotnoacyl bromide 5 converts unreacted carboxylic acid 1 by an exchange reaction into the more reactive acyl bromide 3, which subsequently becomes a-brominated as formulated above [Pg.160]

I Alpha Bromination of Carboxylic Acids The Hell-Volhard-Zelinskii Reaction... [Pg.849]

The Hell-Volhard-Zelinskii reaction is a bit more complex than it looks and actually involves substitution of an acid bromide enol rather than a carboxylic acid enol. The process begins with reaction of the carboxylic acid with PBr3 to form an acid bromide plus HBr (Section 21.4). The HBr then catalyzes enolization of the acid bromide, and the resultant enol reacts with Br2 in an cr-substitution reaction to give an cv-bromo acid bromide. Addition of water hydrolyzes the acid bromide in a nucleophilic acyl substitution reaction and yields the a-bromo carboxylic acid product. [Pg.849]

Problem 22.6 If methanol rather than water is added at the end of a Hell-Volhard-Zelinskii reaction, an ester rather than an acid is produced. Show how you could cany out the following transformation, and propose a mechanism for the ester-forming step. [Pg.849]

Amino acids can also be prepared by a two-step sequence that involves Hell— Volhard-Zelinskii reaction of a carboxylic acid followed by treatment with ammonia. Show how you would prepare leucine, (C bCHCl-HClKNPfylCC H, and identify the mechanism of the second step. [Pg.876]

Heat of combustion, 113 Heat of hydrogenation, 186 table of, 187 Heat of reaction, 154 Helicase, DNA replication and, 1106 Hell-Volhard-Zelinskii reaction, 849 amino acid synthesis and. 1025 mechanism of, 849 Heme, biosynthesis of, 966 structure of, 946 Hemiacetal, 717 Hemiketal, 717 Hemithioacetal, 1148 Henderson-Hasselbalch equation,... [Pg.1300]

In order to introduce an S03 group into long-chain fatty acids, direct sulfonation with sulfur trioxide had been suggested in 1962 [29], similar to the Hell-Volhard-Zelinskii reaction of the a-bromation studied by Watson [34], Ten years previously de Boer had reviewed this mechanism among others for lower aliphatic sulfocarboxylic acids [35]. The sulfonation process was proposed as a two-step mechanism. The first step is the rapid addition of the S03 into... [Pg.464]

The Hell-Volhard-Zelinskii reaction involves formation of an intermediate acid bromide enol, with loss of stereochemical configuration at the chirality center. Bromination of (/ )-2-phenylpropanoic acid can occur from either face of the enol double bond, producing racemic 2-bromo-2-phenylpropanoic acid. If the molecule had a chirality center that didn t take part in enolization (Problem 22.33), the product would be optically active. [Pg.594]

Alpha bromination (Hell-Volhard-Zelinskii reaction) (Sec. 22.4)... [Pg.868]

Hell-Volhard-Zelinskii reaction (Section 22.4) the a-bromination of a carboxylic acid by treatment with bromine and phosphorus tribromide. [Pg.880]

The first step in the Hell-Volhard-Zelinskii reaction takes place bet PBra and a carboxylic acid to yield an intermediate acid bromide plus] (Section 21.4). The HBr thus formed catalyzes enolization of the acid I mide, and the resultant enol reacts rapidly with Brg in an a-substittttif reaction. Addition of water results in hydrolysis of the a-bromo acid 1 mide (a nucleophilic acyl substitution reaction) and gives the n-bromo< boxylic acid product. [Pg.910]

The Hell-Volhard-Zelinskii Reaction 909 Acidity of Alpha Hydrogen Atoms Enolate Ion Formation Reactivity of Enolate Ions 915... [Pg.14]

See also in sourсe #XX -- [ Pg.159 , Pg.160 ]

See also in sourсe #XX -- [ Pg.777 ]

See also in sourсe #XX -- [ Pg.159 , Pg.160 ]

See also in sourсe #XX -- [ Pg.590 ]

See also in sourсe #XX -- [ Pg.849 ]

See also in sourсe #XX -- [ Pg.849 ]

See also in sourсe #XX -- [ Pg.367 ]

See also in sourсe #XX -- [ Pg.702 ]

See also in sourсe #XX -- [ Pg.876 , Pg.877 ]

Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...