Thioformaldehyde trimer

The reaction between PCI3 and thioformaldehyde trimer leads to a low yield of (chloromethyl)phosphonothioic dichloride, a behaviour qualitatively reminiscent of that of the trichloride towards paraformaldehyde (Chapter 3, Section II.A.7). 

Although there are no reported polymerizations of simple cyclic sulfides of ring size 5 and higher, polymerizations of 1,3,5-trithane (the cyclic trimer of thioformaldehyde) (LX), disulfides such as l-oxa-4,5-dithiacycloheptane (LXI), and trisulfides such as norhonene trisulfide (LXII) have heen achieved [Andrzejewski et al., 1988 Baran et al., 1984 Moore et al., 1977 Zuk and Jeczalik, 1979]. 

Monomeric thioaldehydes have not been isolated, although several, e.g. thioformaldehyde, have been identified by photoelectron spectroscopy. The thione group is relatively unstable in the monomeric form (1), and thioaldehydes can only be isolated as dimers (2), trimers (3) polymers (4), or enol derivatives (5), (Scheme 1). 

Thioformaldehyde and symmetrical thioketones can be obtained in only one trimeric form, but unsymmetrical thioketones are obtained in two isomeric forms In the u- or cis-form all three groups R (and, of course, similarly R ) lie on one side of the ring in the / - or trans-form two of a kind lie on one side with the third on the other. This isomerism is naturally prevented if these substituents are too bulky. The cis-compounds can be rearranged catalytically to the more favored, higher-melting / -forms.395"397... 

The simplest chain structure -f-CH2—S- occurs through the polymerization of thioformaldehyde, CH2S, or its cyclic trimer (trithiane). Aliphatic polysulfides with two or more carbon atoms per monomeric unit are available through the polymerization of cyclic sulfides. The start step with organolithium compounds deviates from that of the epoxides in that initially the sulfur atom is attacked and subsequently the carbon atom is attacked. For example, the starting step with propylene sulfide and ethyl lithium initially gives propylene and lithium ethane thiolate ... 

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