molar equivalent of SOCl, under prcssure at 150" for 5 to 8 h yields phosphonic dichlorides in quantitative yield. I n addition sulfur and sulfur clichloriclc is formed according to thc cquation :
,RP(S)CI,+ SOClz+ RP(O)CI,+ X I , + S This method is particularly useful for thc preparation of CH,P(0)C12 since it was observed that chlorination of CH,3P(0) (OCH,), with l'ClS yields Clβ¬,OP(O)Cl, as a by-product which is difficult to separate from CH3P(0)CI,. On thc other hand chlorination of methylphosphonic acid with l'Cls also gives pure CH,P(O)Cl,.
CH,P(O)(OH), + 2 PCl, + CH,P(O)Cl, + 2 HCI+2 POCl, Several methods have been described in the literature for the preparation of phosphonic diclilorides [Z]. One of the most widcly used procedure consists in the conversion of phosphonates to phosphonic dichlorides by reaction with PC1, [Z] .
This reaction is, however, not as clean as given in the equation : RI'(Oj(OR'jz + PCI, 4 RP(O)Cl, + 2 POC1,+ 2 R'CI Often considerable amounts of ester-chlorides, KP(O)Cl(OR) [3] and other com-
pounds are formed which are difficult to separate from the dichlorides. For example, we observed that whcn dimethyl-niethylphosplionate, CH,P(O) (OCH,), was treated with PC1, using POC1, as solvent, considerable amounts of CH,OP(O)Cl, were formed as by-products which could not be separated by fractional distillation from CH,P(O)-
We therefore hydrolyzed the phosplionates first to the acid and then chlorinated the acids with PC1, to the dichlorides as described in the literature [4]. In this way pure CH,P(O)Cl, was obtained.
2 β¬'a5
Similarly, C,H$(O)Cl, was also prepared in this way. This procedure is, however, somewhat lengthy and troublesome and therefore a sinipler method was'sought.
Recently, methyl and ethyl-thiophosphonic diclilorides became commercially available z). Thercfore attempts were made to convert these thiophosphonic dichlorides in one step to phosphonic chlorides. CII,P(O)(OCH,), $. 2 HCI + ZCE1,Cl + CH3P(0)(OH)2 -.---+ CH,P(O)CI, + 2 HCl+2 I'OC1, l)