Cyclotris

With respect to reaction mechanism, it is likely that CpCo(CO)2-mediated alkyne cyclotrimerizations proceed through discrete orga-nometallic intermediates and are therefore not concerted.12 A plausible mechanistic pathway for the CpCo(CO)2-catalyzed cyclotri-... 

Calcichrome. This indicator, cyclotris-7-( l-azo-8-hydroxynaphthalene-3,6-disulphonic acid), is very selective for calcium. It is in fact not very suitable as an indicator for EDTA titrations because the colour change is not particularly sharp, but if EDTA is replaced by CDTA (see Section 2.26), then the indicator gives good results for calcium in the presence of large amounts of barium and small amounts of strontium.13... 

Pb Azide (LA), which is the most important expl used in detonators (Ref 11), although extremely sensitive to shock, heat, and friction, is not sufficiently sensitive to stab action to insure 100% reliability in firing from the stab action. Consequently, the priming mixt is used as a first-fire layer in these units. RDX (cyclotri-methylenetrinitramine), also known as Cyclo-nite, is contained as the output charge of the typical stab detonator. Its output results in a detonation of other expls (Ref 11)... 

Male and female rats showed no treatment-related gross or histological reproductive tract alterations when exposed by inhalation 6 hours/day, 5 days/week for 3 weeks to a 990 mg/m3 aerosol of cyclotri-phosphazene (Kinkead et al. 1989a, 1990), or aerosol concentrations of Skydrol 500B-4 <300 mg/m3,... 

For example, with R R H, reaction (6) gives only oligosilazanes with R CH3 and R = H, both cyclic and oligosilazanes are formed and with R1 > CH3 and R H then one obtains mostly cyclotri- and cyclotetrasilazanes as the products. 

For reactions where R1 = H or CH3, R = H and R = CHo, the products can be mostly linear oligosilazanes depending on conditions (see below) (21-23). The preference for cyclotri- and cyclotetrasilazanes, in these reactions, is not surprising given that the hydrolysis of dihalosllanes also leads to cyclotri- and cyclotetra-siloxanes. 

Base and acid catalyzed ring opening polymerization of cyclotri-siloxane, -[Me2SiO]3- [e.g. reaction (10)], is a well-known method of generating high molecular weight polysiloxanes. 

A number of groups have attempted to develop the analogous reaction for cyclotri- and cyclotetrasilazanes. Ring opening polymerization represents an alternative to direct ammonolysis even though the cyclomer precursors are normally made by ammonolysis or aminolysis. 

Thus, Andrianov et al. (26) attempted to catalyze polymerization of a number of alkyl and alkyl/aryl cyclosilazanes using catalytic amounts of KOH or other strong bases at temperatures of up to 300°C. In general, the reactions proceed with evolution of NHj, hydrocarbons and the formation of intractable, crosslinked, brittle products even at low temperatures. Contrary to what is observed with cyclotri-siloxanes, no evidence was found for the formation of linear poly-silazanes. Copolymerization of mixtures of cyclosilazanes and cyclosiloxanes gave somewhat more tractable polymers with less evolution of hydrocarbons or ammonia, however very little was done to characterize the resulting materials. 

They find that heating cyclotri- and cyclotetrasilazanes with ammonium halide catalysts at temperatures of 160°C for 6-8 h results in a condensation polymerization process that evolves ammonia and leads to the formation of waxy polysilazanes. Analytical results suggest that these polysilazanes consist of rings linked by silyl bridges as illustrated by the following structure ... 

R. Kaufman and R. S. Sidhu, Synthesis of aryl cluster glycosides by cyclotri-merization of 2-propynyl carbohydrate derivatives, J. Org. Chem., 47 (1982) 4941 1947. 

Table . PNMR Spectral data for selected persubstituted cyclotri and tetraphosphazenes"...

The chemistry of cyclophosphazanes is dominated by four-membered rings six-membered P3N3 rings are far less common. The first examples of cyclotri-phosphazanes (MeNPX)3 (X = Cl, Br) were prepared by the cyclocondensation... 

OjMgjCjnHji, Magnesium, cyclotri[p-l,2-phenylenebis(methylene)]hexakis-(tetrahydrofuran)tri-, 26 147... 

Note R-Salz is Cyclotrimethylenetrinitrosa-mine, which.is described in Vol 3 of Encycl, p C630-R. RDX is described as Cyclotri-methylenetrinitramine on pp C626ff... 

Acetoneperoxide, Trimeric or Triacetone Triperoxide (Acetonetriperoxide, Trimeric Acetoneperoxide, Acetonetrimer Peroxide, Cyclotri ace tone Peroxide, or Tricycloacetone Peroxide)(CalIed by Wolfenstein Tricyclo-aceton-superoxyd and by Rohrlich and Sauer-milch Trizycloazetonperoxyd),... 

Note Prepn of Na methoxide reagent is described in Ref 2, p 4 and under Cyclotri-methylenetrinitramine, Analytical Procedures Refs 1)US Joint Army-Navy Spec, JAN-C-427 (1946) (Composition C-3) 2)S.M.Kaye,... 

All attempts to nitrate CTMTU (Cyclotri-methylenetriurethane) and thus convert it to RDX failed... 

The six-membered cyclotri- and the eight-membered cyclotetrasilazanes were the first well-defined silicon-nitrogen rings. They were prepared by Brewer and Haber by ammonolysis of dimethyldichlorosilane in 194813 (Scheme 1). 

B. Isomeric Cyclotri- and Cyclodisilazane-Anions and -Dianions, DFT Calculations... 

Equilibrium between Silyl-Substituted Cyclotri- and Isomeric Cyclodisilazane-Anions... 

Similar trends are observed for the metal complexes prepared in the present study. The mode of coordination of cyclophosphazenes to transition metal ions mainly depends upon the ring size and the nature of the substituent. The rigid six-membered cyclotri-phosphazenes have low propensity for forming metal complexes and clearly steric effects predominate. 

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