The purpose of this chapter is to review the history of plastics, describe the different kinds of plastics, their applications and their benefits, giving several examples of plastics found in our daily lives. The current chapter also provides deep insight into the qualitative characteristics of plastics, while describing their chemical nature in simple terms.

The desaurin 2. whose stereochemistry has now been established by an X-ray crystal structure analysis. can be used as a thioketene equivalent (E).Reactions have been carried out with sodium azide/dimethyl sulfate, N.N-diethylaminopropyne. N-methyl benraldimine. tert-butyl isonitrile and NaN3/CS2 to give the products listed in Schemes I. IV and V. Simple thioketenes (e.g. 16) react analogously with tert-butyl isonitrile. but not with imines where C-C adducts are formed instead of C-S adducts.Dimeric acylthioketenes have been known since the last century and constitute a class of remarkably stable, high melting-point compounds. They are commonly called desaurins because the first derivative, prepared by #eyer from the sodium salt of deoxybenzoin and thiophosgene,' has a beautiful golden colour. A general method of preparation involves the base-catalyzed reaction of carbon disulfide with active methylene compounds to give dithiolate anions, which are subsequently converted into desaurins thermally or by the presence of oxidizing (I2, BrZ, S208For instance, 2,4-bis~cyanomethoxycarbonylmethylene)-1,3-dithietane 2 is obtained as white crystals in 60-700 yield from cyanoacetic ester 1. via the dithiolate anion 2. -) or acylating reagents (oxalyl chloride, phthalyl chloride). 2 -Since the stereochemistry of 2 has not been described in the literature, we have determined its crystal structure. The molecule possesses a crystallographic centre of symmetry, indicating that the 1,3-dithietane ring must be planar and the stereochemistry trans. The a,d-unsaturated carbonyl system is in an s-cis conformation and is coplanar with the ring (see Table 1). This results in a S1...05 distance of 2.74(4) f , considerably shorter than the sum of the van der Waals radii for sulfur and oxygen (3.2 f ) .

ABSTRACT.the reagents given in Scheme I. function of 2.other I,3-thiazetidin-2-thiones (2, -R = Ph, Tol) to give the corresponding 1,2,4-dithiazolidine-3-thiones (12 and 14) in high yield.The title compound 2 is transformed into the heterocycles f! -1 by treatment with In all cases, initial nucleophilic attack occurs at the C-SThe facile ring-expansion reaction 2 -+ 2 has been successfully extended t o 4-Imino-1,3-thiazetidin-2-thiones

Das Desaurin (I) reagiert in Form des Thioketens (II) mit NaN3/Me3SO4, mit Diethylaminopropin bzw. mit Methylbenzaldimin zu den Derivaten (III), (IV) bzw. (V).

Durch Substitutions‐ bzw. Ringerweiterungsreaktionen der aus dem Harnstoff (Ia) und Thiophosgen erhältlichen Titelverbindung (IIa) werden die Heterocyclen (III), (IV),(V) und (VIa) dargestellt.