Dialkyl-vinyl phosphates

Between 1948 and 1952 Morris and Van Winkle (1952), Arbuzov and Alimov (1951), and Perkow et al. (1952) investigated independently the reaction of polyhalogen aldehydes, primarily of chloral, with trialkyl phosphites. The conversion was assumed by some workers to be a true Michaelis-Arbuzov reaction and, accordingly, it was thought erroneously that the product formed in the reaction of chloral and trimethyl phosphite is the phosphonate of formula 66. Perkow et al. (1952) established that a-halogen carbonyl compounds give with trialkyl phosphites an anomalous Michaelis-Arbuzov reaction, so that the actual reaction product is 2,2-dichlorovinyl phosphate, 67. This reaction is known in the literature as Perkow s reaction. 

Independent of these workers, Lorenz et al. (1955) found that 0,0-dimethyl-(l-hydroxy-2,2,2-trichloro)ethane phosphonate (trichlorfon, 68), to be discussed later, on interaction with alkali loses one mole of hydrogen chloride, and that subsequent rearrangement also yields product 67 (dichlorvos, DDVP). 

Dichlorvos is a very effective insecticide, used in plant protection against sucking and chewing insects and leaf miners, and in the hygiene sector against flies. It is highly volatile and therefore also has a fumigant action. It is rapidly hydrolysed in plants to dimethyl phosphate and dichloroacetaldehyde, so that it can also be used shortly before harvest. The oral lDjo for rats is 62 mg/kg. 

7-methyl-guanine. However, their assumptions concerning both the mechanism of the alkylation reaction and the mutagenic and carcinogenic effect of dichlorvos, have been disproved by others (Buselmaier et al., 1972 Dean and Thorpe, 1972 Epstein et al., 1972 1975). 

The Perkow reaction of triethyl phosphite with 2-chloroethyl trichloroacetate gives 0,0-diethyl-0-[l-(chloroethoxy)-2,2-dichlorovinyl] phosphate (69), introduced under the trade name Forstenon (Sallmann, 1952). 

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Perkow reaction.1 Perkow2 noted that a-halo aldehydes and ketones react with trialkyl phosphites to give dialkyl vinyl phosphates ... 

In 1952, Perkow reported (242) that a-haloaldehydes did not react with trialkyl phosphites according to the Michaelis-Arbuzov reaction, although this had been repeatedly reported, but that a new type of reaction occurred, yielding dialkyl vinyl phosphates isomeric with the expected phosphonates. 

When performed in ether at —70 °C containing HCl, the reaction between triethyl phosphite and either chloral or bromoacetone affords higher yields of the a-hydroxyphosphonates (34), relative to vinyl phosphate, than are normally obtained. The rate-determining step in the formation of the phosphonate (35) from chloroacetone and dimethyl hydrogen phosphonate appears to be the tautomerism of dialkyl phosphonate to phosphite. ... 

The reaction of sodium dialkyl phosphite with a-halogenokctoncs leads to a mixture of products consisting of P-ketophosphonates, 1,2-epoxyphosphonates, and vinyl phosphates (Scheme The subject has been covered in the Section 4.1.1.2. 

Synthesis of Phosphoric Acids and their Derivatives.-New approaches to the preparation of dialkyl phosphorofluoridates include the treatment of a vinyl phosphate, e.g.,(l), or an irninophosphace, e.g.,(2), with triethylamine tris(hydrogen fluoride) when the alkyl group consists of a suitably protected nucleoside, the reaction between mono(crimethylsilyl) phosphite in pyridine and sulphuryl chloride fluoride at -30° has been successfully explored. Dibenzyl phosphorofluorldate, hitherto unreported, has been obtained from tecrabenzyl diphosphate and caesium fluoride, and also from the reaction between dibenzyl hydrogen phosphate and 2-fluoro-N-methylpyridinlum tosylate. ... 

The Perkow reaction has been used to generate a wide range of vinyl phosphates. Reaction of trialkyl phosphites with a-halogeno-ketones provide vinyl phosphates.1-5 Alkenes are produced via reduction of the dialkyl enol phosphate using either sodium or lithium in liquid ammonia. 

The main applications are with PVC. The plasticizers which can be blended in can be either low MW organic compounds, e.g. dialkyl phthalates, phosphates (tricresyl phosphate which has flame-retardant characteristics) or low-MW polymers, e.g. polycaprolactone, PMMA, or copolymers of ethylene and vinylacetate (EVA). These are called external plasticizers. Internal plasticization can be achieved by copolymerizing VC with a comonomer which has a low Tg, e.g. vinyl acetate. 

Esterification of dialkyl phosphates is carried out with diethyl azodicarboxylate and triphenylphosphine (equation 46). This condensation is applicable to phosphorylation of pyrimidine nucleosides. The trichloromethanephosphonic acid derivative (69 equation 47) serves as a phosphorylating agent of ribonucleosides, affording the 2 - and 3 -monophosphates. ° Ethyl vinyl ether assisted the dimeric condensation of diethyl hydrogen phosphate giving tetraethyl pyrophosphate (equation 48). ... 

Because heteroatom-substituted vinylphosphonates such as enol phosphates and vinyl halides are masked acetylenic compounds, a variety of methods have been developed for their elaboration and subsequent use in the synthesis of dialkyl 1-alkynylphosphonates. These eliminations usually have the leaving group P to the phosphoryl group, although cases in which the leaving group is a to the phosphorus center are also known (Scheme 1.12). 

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