Octamethylcyclotetrasilazane

As already discussed in Section 2.2, crystalline dimethylsilanediol 53 can be prepared by hydrolysis from hexamethylcyclotrisilazane 51, from dimethoxydimethyl-silane [40], and from octamethylcyclotetrasilazane (OMCTS) 52. The most simple preparation of 53 is, however, controlled hydrolysis of dimethyldichlorosilane 48 in the presence of (NH4)2C03 or triethylamine [41]. Likewise, hydrolysis of hexam-ethylcyclotrisiloxane 54 and of octamethylcyclotetrasiloxane 55 eventually gives rise to dimethylsilanediol 53. In all these reactions the intermediacy of the very reactive dimethylsilanone 110 has been assumed, which can be generated by pyrolytic [42, 43] and chemical methods [44—46] and which cyclizes or polymerizes much more rapidly, e.g. in contact with traces of alkali from ordinary laboratory or even Pyrex glassware [40, 47] to 54, 55, and 56 than trimethylsilanol 4 polymerizes to hexamethyldisiloxane 7. Compound 111 is readily converted into dimethylsilanone 110 and MesSil 17 [46] (Scheme 3.6). 

Reaction of 2,4-(lH,3H)-quinazolinedione 250 for 8h at 130°C with two equivalents of N-2-hydroxyethylpiperazine 251 (the alcohol group of which is in-situ protected by silylation), HMDS 2, and catalytic amounts of TSOH H2O, and subsequent transsilylation with boiling methanol, affords 68% of the monoaminated product 252 and methoxytrimethylsilane 13 a. Reaction of 250 with fivefold excess of N-2-hydroxyethylpiperazine 251 in the presence of octamethylcyclotetrasilazane... 

Octamethylcyclotetrasilazane (130) reacts with M-butyllithium or alkaline metals to give the alkali salts, which crystallize as dimeric THF adducts (equation 40). In the dimers, two eight-membered rings are connected by a planar alkali metal-nitrogen four-membered ring. Lithium is tricoordinated, sodium tetracoordinated and potassium penta- and hex-acoordinated. The coordinatively bonded THF in the lithium compound (131) can be exchanged with the Lewis base TMEDA103. 

Dilithiated octamethylcyclotetrasilazane (136) reacts with a difluoroboryl substituted cyclotrisilazane (137) to give the BF coupled 6-8-6-membered cyclosilazane 138 (equation 41 )100. The eight-membered ring has a chair conformation. 

Smith, G. S., and L. E. Alexander Octamethylcyclotetrasilazane, an ordered crystal containing two geometrical isomers. Acta crystallogr. [Copenhagen] 16, 1015—1022 (1963). 

Since HMDS boils at I26°C, and the least reactive silylated 2- H)-pyridinone (27) has to be heated to a much higher temperature to effect conversion, 27 is reacted with the stable crystalline and commercially available octamethylcyclotetrasilazane (OMCTS) (157) (melting point = 97°C, boiling point = 225°C) (57M11) to afford activated dimeric intermediates such as 158, which can be aminated at 180-200°C in the presence of... 

Among the pyrolysis products of plasma-polymerized HMCTSN we found monomer (B), its oxy-derivative (A), octamethylcyclotetrasilazane (C) and bicyclic dimer (E) (Fig. 1 and Table I). It was difficult to identify the structure of compound D, but on the basis of mass spec-trometric data we speculate that it is an unstable product formed by ammonia elimination from the dimer molecule. 

The presence of octamethylcyclotetrasilazane and bicyclic dimer in the pyrolysis products strongly suggests that at least two competitive reactions take place during plasma polymerization of HMCTSN namely, ring enlargement and dimerization. However, dimerization seems to be predominant and it is considered to be the first step of reaction leading to polymer formation. 

Octamethylcyclotetrasilazane, boiling point 134.5 to 135.5° at 35 mm. and 225° at 756 mm., is a white solid which melts at 97°. Octamethylcyclotetrasilazane hydrolyzes in moist air to form ammonia and siloxanes. 

Cyclotetramethylene sulfone. See Sulfolane Cyclotetrasilazane, 2,2,4,4,6,6,8,8-octamethyl-. See Octamethylcyclotetrasilazane... 

See Octamethylcyclotetrasilazane Octamethylcyclotetrasiloxane CAS 556-67-2 EINECS/ELINCS 209-136-7 Synonyms Cyclic dimethylsiloxane tetramer Cyclotetrasiloxane, octamethyl- Octamethyltetracyclosiloxane Classirication Silicone oligomer cyclic siloxane Empirical CsH2404Si4 Formula [(CH3)2SiO]4... 

Octadecyltrichlorosilane Octamethylcyclotetrasilazane Octamethylcyclotetrasiloxane Octamethyltrisiloxane Octaphenylcyclotetrasiloxane Octyidimethylchlorosilane Octyltrichlorosilane Octyltriethoxysilane ... 

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