P-chlorophenyl acetate

The research group of Backvall employed the Shvo s ruthenium complex (1) [21] for the racemization. This complex is activated by heat. For the KR they used p-chlorophenyl acetate as the acyl donor in combination with thermostable enzymes, such as CALB [20] (Figure 4.7). This was the first practical chemoenzymatic DKR affording acetylated sec-alcohols in high yields and excellent enantioselectivities. In the best case 100% conversion (92% isolated yield) with 99% ee was obtained. This method was subsequently applied to a variety of different substrates and it is employed (with a different ruthenium complex) by the Dutch company DSM for the large-scale production of (R)-phenylethanol [22]. 

Incubation of p,p- D hl with hematin and ammonia gave p,p- DW, / ,//-DDE, bis(p-chlorophenyl)acetonitrile, l-chloro-2,2-bis(p-chlorophenyl)ethylene, 4,4 -dichlorobenzophenone, and the methyl ester of bis (p-chlorophenyl) acetic acid (Quirke et al., 1979). 

Bis(/t-chlorophenyl)acetic acid, see p,p -DDT Bis(p-chlorophenyl)acetic acid, methyl ester, see... 

Figure 6.14 DCL-E in presence of PS-C I and p-chlorophenyl acetate (44) (modified from Reference 1).

DKR of secondary alcohol is achieved by coupling enzyme-catalyzed resolution with metal-catalyzed racemization. For efficient DKR, these catalyhc reactions must be compatible with each other. In the case of DKR of secondary alcohol with the lipase-ruthenium combinahon, the use of a proper acyl donor (required for enzymatic reaction) is parhcularly crucial because metal catalyst can react with the acyl donor or its deacylated form. Popular vinyl acetate is incompatible with all the ruthenium complexes, while isopropenyl acetate can be used with most monomeric ruthenium complexes. p-Chlorophenyl acetate (PCPA) is the best acyl donor for use with dimeric ruthenium complex 1. On the other hand, reaction temperature is another crucial factor. Many enzymes lose their activities at elevated temperatures. Thus, the racemizahon catalyst should show good catalytic efficiency at room temperature to be combined with these enzymes. One representative example is subtilisin. This enzyme rapidly loses catalytic activities at elevated temperatures and gradually even at ambient temperature. It therefore is compatible with the racemization catalysts 6-9, showing good activities at ambient temperature. In case the racemization catalyst requires an elevated temperature, CALB is the best counterpart. 

The group of Backvall employed the Shvo s ruthenium complex (1) [45] for the racemization. This complex is activated by heat. For the KR, p-chlorophenyl acetate... 

Chlorobenzilate or ethyl 2-hydroxy-2,2-di-(p-chlorophenyl)-acetate is a chlorinated aromatic a-hydroxy ester. It has an empirical formula of C gH C Og and a molecular weight of 325.18. 

Backvall, in contrast, used the ruthenium complex 1, which does not require the addition of an external base, in combination with p-chlorophenyl acetate as acyl donor (Fig. 9.4). The latter was chosen because it generates p-chlorophenol which does not react with the Ru catalyst. In contrast, vinyl acetate and analo-... 

Di-(p- chlorophenyl)-acetic acid is prepared in 70% yield from l,l-di-(p-chlorophenyl)-2,2,2-trichloroethane, (p-ClC H4)jCHCClj (DDT). This reaction differs from a straightforward hydrolysis since hydrogen chloride is eliminated and an intermediate, l,l-di-(p-chlorophenyl)-2,2-dichloroethyl-ene, (p-ClCgH4)2C = CClj, is readily isolated in 97% yield. ... 

The ruthenium-catalyzed racemization of a-methylbenzyl alcohol was combined with an enzyme-catalyzed transesterification with lipase. Dinuclear ruthenium complex 64 effectively catalyzes the racemization of a-methylbenzyl alcohol and the combination of 64, p-chlorophenyl acetate, and enzyme N-435 in the reaction of racemic amethylbenzyl alcohol gave enantiomerically pure (R)-a-methylbenzyl acetate in the excellent yield (Eq. 12.26) [29]. 

Metabolism of DDT proceeds at a very slow rate. Liver microsomal P450 and other microsomal enzymes initially dechlorinate DDT to l,l-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) and reduce to 1,1 -dichloro-2,2-bis(p-chlorophenyl)ethane (DDD). The conversion of DDD to bis(p-chlorophenyl)acetic acid (DDA) involves the formation of an acyl chloride intermediate by hydroxylation followed by hydrolysis to yield the final product. 

Interaction T)f 1,1,1 -trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) and alkali gives, according to the conditions, either bis-(p-chlorophenyl)acetic acid or 2,2-dichloro-1,1 -bis-(/ -chlorophenyl)ethylene.551... 

BHC—Mixed isomers of 1,2,3,4,5,6-hexachlorocyclohexane Chlordan—l,2,4,5,6,7,10,10-octachloro-4,7,8,9-tetrahydro-4,7-methyleneindane DBH—p,p -dichlorobenzhydrol DBF—p,p -dichlorobenzophenone DDA—bis(p-chlorophenyl) acetic acid DDD—l,l-dichloro-2,2-bis (p-chlorophenyl) ethane DDE—l,l-dichloro-2,2-bis(p-chlorophenyl) ethylene DDMS—l-chloro-2,2-bis (p-chlorophenyl) ethane DDMU—l-chloro-2,2-bis (p-chlorophenyl) ethylene DDNU—1,1-bis (p-chlorophenyl) ethylene DDT—l,l,l-trichloro-2,2-bis(p-chlorophenyl) ethane Dieldrin—l,2,3,4,10,10-hexachloro-6,7-epoxy-l,4,4a,5,6,7,8,8a-octahydro-... 

B.D. Banerjee, Development of an Enzyme-linked Immunosorbent Assay for the Quantification of DDA (2,2-bis (p-Chlorophenyl) Acetic Acid) in Urine , Bull. Environ. Contam. Toxicol, 38, 798 (1987). 

DI-(p-CHLOROPHENYL)-ACETIC ACID (Acetic acid, di-(p-chlorophenyl))... 

The Hammett eqnation is the best known and most widely stndied of the various linear free energy relations for correlating reaction rate and equilibrium constant data. This equation was first proposed to correlate the rate constants and equilibrium constants for the side chain reactions of para- and me/a-substituted benzene derivatives. Hammett (37-39) noted that for a large number of reactions of these compounds plots of log k (or log K) for one reaction versus log k (or log K) for a second reaction of the corresponding member of a series of such derivatives was reasonably linear. Figure 7.5 is a plot of this type involving the ionization constants for phenylacetic acid derivatives and for benzoic acid derivatives. The point labeled p-C has for its ordinate log for p-chlorophenyl acetic acid and for its abscissa log for p-chlorobenzoic acid. 

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