Polyhalogen compounds preparation

Products containing two or more phosphorous acids can be prepared from polyhalogenated compounds see Eq. (30). 

A number of preparatively useful reductions with removal of halogen was discussed in Part I. Often a stepwise removal of the halogens takes place in a polyhalogenated compound. 4-Methyl-2,6-dichloropyrimidine (288) thus gives three peaks in DMF, the third peak being the reduction of the nucleus. Preparative reduction at the potential of the first peak affords 4-methyl-2-chloropyrimidine436 [Eq. (148)]. 

It is well established that hydrogen forms more than one covalenl binary compound with carbon. Fluorine behaves similarly. Thus, fluorine forms CFi. C>F4. CjFV,. C.rFx and many higher hontologs. as well as the definitely imerstiiial compound (CF) . The other halogens form some similar compounds, although 10 more limited extent, and various polyhalogen compounds have been prepared. They exhibit the maximum covalencv of four and are therefore inert to hydrolysis and most other low temperature chemical reactions. 

The dehydrohalogenation of 1,1-dichloro- and 1,1-dibromocyclopropanes to 1-halocyclopropenes has in some cases been of value, and has been applied in particular to the preparation of polyhalogenated compounds ... 

A similar synthetic scheme was adopted by Nadel [13] to prepare isothiazolones 34 and 35 from L-cystine derivatives transformed into the corresponding cystine fozs-N-(methylamides) 33a-c (Et0C02Cl, TEA in CH2CI2 then MeNH2/H20, 69- 73%) (Scheme 10). As reported in Table 1, several parameters were evaluated in order to find the best reaction conditions to produce the different isothiazolone derivatives 34 (43-63%) or 35 (52-66%). As by-products, the polyhalogenated compounds 36 and 36 (not separable) were formed in some instances. Finally, the deprotection of the amino group... 

This compound was first prepared in some noteworthy studies by R. West from tetralithiopropyne and chlorotrimethylsilane. We have observed the formation of the allene from reaction of lithium and chlorotrimethylsilane with a great variety of polyhalogenated compounds. The diversity of transformations is very large, and the number of exceptional reactions is also great. 

From polyhalogenated alkanes it is possible to prepare compounds containing more than one aromatic ring ... 

The existence of polyhalogen cations seems well establislied. Some eation-anion interaction takes place, but nevertheless theii structure is basically ionic. In Oiis review, the preparations, properties and structural data of tiiese compounds are summarized and discussed. 

Polyhalogen cations of aU these types have indeed been prepared and studied. All these compounds are usually highly hygroscopic and hydrolyze easily, and must therefore be handled and kept under dry conditions. 

In summary, it seems that most of the possible polyhalogen cations have indeed been prepared and identified. Their chemistry is rather diversified and various modem physical methods have been used in determining their structures and properties. Some interesting data, such as particular single-crystal X-rays are still missing. Most of all, it would be interesting to study more carefiilly possible chemical applications and reactions of these highly reactive compounds. 

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