Amine promoters

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

Both the equilibria and the enhancement of the coefficients can be improved by additives, of which sodium arsenite is the major one in use, but sodium hypochlorite and small amounts of amines also are effective. Sterically hindered amines as promoters are claimed by Say et al. (Chem. Eng. Prog., 80(10), 72-77 [1984]) to result in 50 percent more capacity than ordinary amine promoters of carbonate solutions. 

Catalytic coupling reaction of aldehydes, alkynes, and secondary amines promoted by less than 3 mol.% of Ag(l) salt was reported by Li et al,517 In this reaction, pure water was used as solvent and Agl was found to be the best catalyst without need of any additives or co-catalysts (Table 9). The reaction mechanism has been proposed as shown in Scheme 110. 

Table 12 Water-gas shift rates between hydroxide and amine promoted catalysis77...

Secondary aliphatic amines were found to give higher yields of thienothiophenes than did tertiary amines, which are weaker bases. A maximum ratio of thienothiophenes to thienothiopyrans of about 4 1 was achieved at 145° with diisopropylamine as cat yst and DMSO as solvent. Only thienothiopyrans were formed in DMF in the presence of the same catalyst The amines promote nucleophilic cyclization of Claisen rearrangement products into thienothiophenes. Since thienothiophenes are resistant to treatment with potassium t-butoxide in DMSO and thienothiopyrans form resinous products under these conditions, the method is a convenient route to pure thienothiophenes 35 and 42 in yields of up to 40%. ... 

Amine promoters tend to give higher acetaldehyde rates relative to phosphines. Increasing the temperature to 200 increases the rate to 7.1 M/hr whereas decreasing the pressure to 2000 psig markedly lowers the rate. Lil is a critical component of the catalyst. Substituting Lil with Nal, KI, or CH I results in a substantial loss in catalytic activity. A key step in the postulated reaction mechanism, as outlined in Equations 16-18, is cleavage of methyl acetate by Lil to yield CH I and LiOAc (27). ... 

These include water-based materials such as amine, esters and alkylsilanes. Water-based amines and esters have no significant effect on slump and rate of hardening of concrete. It is claimed they delay corrosion of steel both in cracked and uncracked members. Effectiveness of the admixture has been attributed to a dual mechanism of corrosion inhibition, viz. prevention of chloride and moisture ingress and formation of a protective film on the surface of the steel. Ester molecules derived from the admixture are said to line the pores of the concrete thus increasing the resistance to moisture and chloride penetration, while the film-forming characteristics of the amine promote adsorption of the molecules on the steel surface, providing a protective coat which keeps moisture and chlorides out. 

Aminocarbonylation has been combined with the Pauson-Khand reaction to construct fused tricyclic alkaloid skeletons (see 00154). The tandem aminocarbonylation/Pauson-Khand reaction of haloalkynes with a chiral allylic amine promoted by Co2(CO)8 gave angular triquinanes as exemplified in Scheme 25. Thus, the reaction of l-chloro-2-phenylethyne 175 with Co2(CO)8 at 0°C gave alkyne-dicobalt complex 176, which was converted to enoyl-dicobalt complex 177 upon warming to 25 °C. The reaction of enoyl-dicobalt complex 177 with cyclopente-nylmethyl(l-phenylethyl)amine 179 yielded Pauson-Khand reaction product, angular triquinane 180, via A -allylic aminocarbonylated alkyne-dicobalt complex 178 (Scheme 25). ... 

Changes in reaction temperature and solvent dielectric constant are expected to affect the equilibria (30)—(32), and such effects are indeed observed (108). The addition of salts as promoters can also alter the optimum amounts of amine promoters to be used. 

V-Methylpyrrolidone was noted by Keim el al. (39) to be a good solvent for CO hydrogenation by rhodium catalysts in the absence of added promoters. The basicity of the compound [p BH + = — 0.9 (45)] probably allows it to serve the same function as weakly basic amine promoters. The high... 

Thiochrom-4-ones have also been prepared by the amine-promoted elimination of hydrogen halide from 3-haIothiochroman-4-ones,188 by the Puinmerer reaction on thiochroman-4-one S-oxides [Eq. (20)],98 from a ring expansion of activated benz[6]thiophenes [Eq. (21)],189 by the reaction of o-mercaptoaryl alkyl ketones with ethyl esters of... 

In contrast to cobalt, rhodium permits a one-step oxo alcohol synthesis in the presence of certain monomeric and polymeric amines (8, 9, 10). Included in this group are triethylamine, N-alkylpiperidines, N-methylpyrrolidine, and N,N-dimethylbenzylamine (DMBA). Initial kinetic data on this amine-promoted alcohol synthesis (under severe reaction conditions) have been reported by B. Fell and coworkers (II), but no attempt has been made to characterize the catalytic species in the reaction cycle. 

Species II and III (Reaction 3) were postulated to account for the catalytic behavior of these systems species II, for the amine-promoted hydrogenation activity, and species III, for continued hydroformylation activity in the presence of amine. In continuous flow experiments on polyDMBA catalysts, rhodium retention was reported to be good (9) with... 

Scheme 28 Opening of P-lactam ring with amines promoted by the Et3N/DMAP system...

Scheme 43 Amine promoted transformation of a-keto P-lactams to a-amino acid derivatives...

The high element effects for the reactions of amines with (11) and (12) suggest multiplicity of mechanistic routes. The second-order kinetics and the very slow exchange of cis-bromo-(ll-a-D) in isopropanol fit addition-elimination (Ghersetti et al., 1965). In methanol, exch/ nub values for reaction of cyclohexylamine with cis and iraws-chloro-(ll) and cis- and Jrans-bromo-(ll) are 13, 11, 20 and 23, respectively, and 0-9, 0-6, 1 4 and 0-8 for the corresponding reactions of di-n-butylamine. While (rans-bromo-(ll) and cis-chloro-(ll) showed normal kinetics in methanol and in ethanol, the rate constants with cis-bromo- (11) and (12) decreased with time, but steady second-order behaviour could be achieved by addition of the perchlorate of the amine used. While this fits an amine-promoted elimination-addition, where the ammonium salt formed shifts the equilibrium to the left (equation 15), the slow... 

Scheme 12. Proposed mechanism for the amine-promoted iron-catalyzed homologations of alcohols. From Ref. 127.

Treatment of 7 with secondary amines, such as dimethylamine or pyrrolidine, in tetrahydro-furan gives uracil derivatives 10, in 87% and 73% yield, respectively105. The overall reaction course for the two nucleophilic attacks with secondary amines is similar to that for ammonia or primary amines, except that the 2, 3 -ribo-aziridinium is the transitional intermediate formed with the secondary amines promoting a third nucleophilic attack by the C-2 oxygen to give the stable 3 -deoxy-3 -substituted-2,2 -0-anhydrouridine derivatives 10. 

While most nucleophiles react with the fused thiiranium salt at carbon (Section 1.06.6.5), certain soft nucleophiles including anion of malonate ester, iodide, thiourea, phosphines, and tertiary amines promote elimination of the sulfur atom by nucleophilic attack on sulfur (Scheme 36) <1980T1361>. 

For the most part, vinyl halides are unreactive however, a few have been converted to vinyl-type cyanides under conditions employed for aromatic halogen compounds. Thus, sym-diiodoethylene has been converted by cuprous cyanide with an amine promoter to fumaronitrile (74%). The halogen atom in certain triarylvinyl bromides has also been replaced by the cyano group under these conditions. ... 

Catalytic multicomponent synthesis of highly substituted pyrroles has been described. A one-pot reaction uses DBU with the commercially available thiazolium salt 513 to produce the necessary nucleophilic zwitterionic catalyst in situ, which promotes a conjugate addition of acylsilanes (sila-Stetter) and unsaturated ketones to generate 1,4-dicarbonyl compounds in situ. Subsequent addition of various amines promotes a Paal-Knorr reaction, affording the desired polysubstituted pyrrole compounds in a one-pot process in moderate to high yields (Scheme 129) <2004OL2465>. Microwave heating dramatically reduced the reaction time (from 16 h to 30 min), but offered no improvement in yields. 

Several types of additives have been found which reduce or eliminate the effects of various catalysts in polyurethane formation. When the catalyst is a simple base, an acid or acid precursor such as an acid chloride will reduce the rate of reaction due to neutralization of the basic catalyst. This is often most desirable, since many of the bases stronger than tertiary amines promote side reactions such as trimerization, carbodiimide formation and allophanate formation. The beneficial effect of acid retarders in a variety of systems was illustrated by Heiss et al. [151], as well as by others. 

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