Trimer Syntheses

Formation of Heavy Transition Metai Group VI Metai-Metal Bonds 79 9.2.9.6. Group VI Trimers with Metai-Metai Bonds 9.2.9.6.1. Moiybdenum Trimer Syntheses. 

Fig. 11.1 Stractures of fully reacted cyanurates along with their molecule wights, bulk Tg, Tg depression, and difference Tg2-Tgi, including a cyanurate trimer synthesized m a mono iw tional cyanate ester, a polycyanurate from a mixture of mono- and di-function cyanate es ers, a polycyanurate network from a dicyanate ester. After Refs. [30, 32-34]...

Although both dimer and trimer are known to exist, the trimer is the more easily produced. Typically, the dimer is only seen as a by-product of the trimer synthesis. Unfortunately, over the past decade law enforcement agencies have encountered TATP more frequently both in the United States and abroad. Numerous questions regarding its synthesis and properties have surfaced in Internet news groups as well, and there is no sign of abatement in interest about the compound. 

Group VI Trimers with Metal-Metal Bonds 9.2.9.6.2. Tungsten Trimer Synthesis. 

Fig. 2. (a) Trimer synthesis, (b) the ring-opening polymerization, and (c) the macromolec-ular substitution. 

Fig. 2 Polyphosphazene synthesis scheme developed by Allcock a trimer synthesis, b ringopening polymerization, and c macromolecular nucleophilic substitution...

The effect of the presence of PCI5 was studied as this might be carried over from the trimer synthesis chemistry. PCI5 was found to inhibit the polymerization, and... 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequendy used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkaU catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonittile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkaU metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Grignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

Synthesis. The synthesis of poly(dichlotophosphazene) [25034-79-17, (N=PCl2) (4), the patent polymer to over 300 macromolecules of types (1) and (2), is carried out via controlled, ring-opening polymerization of the corresponding cycHc trimer, (N=PCl2)3 [940-71 -6]. 

Reportedly, simple alkyl isocyanates do not dimerize upon standing. They trimerize to isocyanurates under comparable reaction conditions (57). Aliphatic isocyanate dimers can, however, be synthesized via the phosgenation of A[,A[-disubstituted ureas to yield /V-(ch1orocarhony1)ch1oroformamidine iatermediates which are subsequendy converted by partial hydrolysis and base catalyzed cycUzation. This is also the method of choice for the synthesis of l-alkyl-3-aryl-l,3-diazetidiones (mixed dimers of aromatic and aUphatic isocyanates) (58). 

Ketene trimer can be recovered from the tarry residue of diketene distillation and converted into valuable building blocks like 1,3-cyclobutanedione and squaric acid [2892-51-5] (140,141), an important intermediate in the synthesis of pharmaceuticals and squaryHum dyes used in photostatic reproduction (142,143). 

DL-Alk-2-enopyranos-4-uIose, 2,3-dideoxy-synthesis, 1, 426 Alkoxy nitroxide radicals pyridines ESR, 2, 146 Alkyl cyanides trimerization, 3, 503 Alkylating agents as pharmaceuticals, 1, 157 Alkylation... 

Piperidine, 3-aryIoxymethyI-4-phenyI-as antidepressant, 1, 169 Piperidine, JV-bromo-photoelectron spectroscopy, 2, 142 Piperidine, cis-4- t-butyl-r- cyclohexyl-1 -phenyl-X-ray analysis, 2, 161 Piperidine, 3-chloro-pyrrolidines from, 4, 147 Piperidine, N-chloro-photoelectron spectroscopy, 2, 142 reactions, 2, 373 trimerization, 3, 510 Piperidine, 4-cycIopentyI-2,6-dioxo-synthesis... 

The use of azide reagents is also important for the synthesis of cyclic sulfur(VI)-nitrogen systems. The reaction of SOCI2 with sodium azide in acetonitrile at -35°C provides a convenient preparation of the trimeric sulfanuric chloride [NS(0)C1]3 (Eq. 2.16). " Thionyl azide, SO(N3)2 is generated by the heterogeneous reaction of thionyl chloride vapour with silver azide (Eq. 2.17). This thermally unstable gas was characterized in situ by photoelectron spectroscopy. The phenyl derivative of the six-membered ring [NS(0)Ph]3 can be prepared from lithium azide and PhS(0)Cl. ... 

The hydroxyl derivative of X-CN is cyanic acid HO-CN it cannot be prepared pure due to rapid decomposition but it is probably present to the extent of about 3% when its tautomer, isocyanic acid (HNCO) is prepared from sodium cyanate and HCI. HNCO rapidly trimerizes to cyanuric acid (Fig. 8.25) from which it can be regenerated by pyrolysis. It is a fairly strong acid (Ka 1.2 x 10 at 0°) freezing at —86.8° and boiling at 23.5°C. Thermolysis of urea is an alternative route to HNCO and (HNCO)3 the reverse reaction, involving the isomerization of ammonium cyanate, is the clas.sic synthesis of urea by F. Wohler (1828) ... 

The process can be still more simplified. It is not always necessary to use a pre-formed Schiff s base. Often it is sufficient to bring the carbonyl compound and the amine together in an inert solvent and to add the peracid to the mixture later, - In this way oxaziranes can be obtained in good yield even if the Schiff s base is unknown or can only be obtained in poor yield. For example, formaldehyde gives with aliphatic amines usually only trimers of the Schiff s bases (4). On the other hand, the synthesis of 2-cyclohexyl-oxazirane (5) from cyclohexylamine, formaldehyde, and peracetic acid proceeded in 66%... 

The main use of acrolein is to produce acrylic acid and its esters. Acrolein is also an intermediate in the synthesis of pharmaceuticals and herhicides. It may also he used to produce glycerol hy reaction with isopropanol (discussed later in this chapter). 2-Hexanedial, which could he a precursor for adipic acid and hexamethylene-diamine, may he prepared from acrolein Tail to tail dimenization of acrolein using ruthenium catalyst produces trans-2-hexanedial. The trimer, trans-6-hydroxy-5-formyl-2,7-octadienal is coproduced. Acrolein, may also he a precursor for 1,3-propanediol. Hydrolysis of acrolein produces 3-hydroxypropionalde-hyde which could he hydrogenated to 1,3-propanediol. ... 

Simidzu et al.70) carried out template-directed synthesis using various types of templates, e. g neutral ones, 34 (PSt TCT) and PSt TCTC, and cationic ones, such as APVP, 35 (APVP PSt), UPVP PSt, ARPVP, APEI, and 36 (ARPEI). They obtained a large amount of purine-containing oligomers (dimer or trimer) as compared to pyrimidine ones by condensation of nucleotide mixture in the presence of the neutral templates containing pyrimidine bases, such as PSt TCT and PSt TCTC. The authors stated from the results that the existence of the... 

Heterocyclic block copolymers, 282-284 Heterocyclic diamines, rigid, 281 Heterocyclic polymers, structure-property relationships in, 273-274 Heterocyclic ring formation, PQ and PPQ synthesis by, 309-310 Hexadecyltrimethylammonium bromide (HTMAB), 549-550 Hexamethylene diisocyanate (HDI), 199, 210. See also HDI trimer Hexamethylenediamine-adipic acid salt, 169, 170... 

Trimer foams, 201 Trimerization, 226-227 Trimethylol propane (TMP), 224 Trimethylsilyl 3,5-diacetoxybenzoate, synthesis and polycondensations of, 118... 

Controlled synthesis and detailed characterization of triblock copolymers of di-phenylsiloxane and dimethylsiloxane has been reported by Meier and co-workers147 148), who used lithium based initiators and the cyclic trimers of dimethyl and diphenyl-... 

A structurally related tetrameric macroheterocycle is compound 13 that is prepared in a one-pot synthesis (yield 64%) from salicylaldehyde and (3-aminophenyl)boronic acid in methanol (Fig. 4). Due to its insolubility it has been characterized only by mass spectrometry. If a substitutent is introduced at the imine function (R = Me, Ph), trimeric structures (14 and 15) are... 

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