Amines as catalysts

Similarly, carbon disulfide and propylene oxide reactions are cataly2ed by magnesium oxide to yield episulftdes (54), and by derivatives of diethyUiac to yield low molecular weight copolymers (55). Use of tertiary amines as catalysts under pressure produces propylene trithiocarbonate (56). 

Benzal chloride is hydrolyzed to benzaldehyde under both acid and alkaline conditions. Typical conditions include reaction with steam in the presence of ferric chloride or a zinc phosphate catalyst (22) and reaction at 100°C with water containing an organic amine (23). Cinnamic acid in low yield is formed by heating benzal chloride and potassium acetate with an amine as catalyst (24). 

This reaction pathway explains well the applicability of amines as catalysts. There is evidence for each one of the mechanisms outlined above. Because of the wide scope of the reaction, there may be no uniform mechanism that would apply to all cases. 

The procedure is illustrative of a general method of ethylating amines, wherein one reacts the amine with ethylene using an alkali-metal salt of the amine as catalyst.2 Di- -butylamine and -hexylamine have been thus ethylated at 130-160°, aniline, o-toluidine, and N-methylaniline at 240-275°. In general, higher olefins add to amines only sluggishly.2... 

Organic-Base Catalyzed. Asymmetric direct aldol reactions have received considerable attention recently (Eq. 8.98).251 Direct asymmetric catalytic aldol reactions have been successfully performed using aldehydes and unmodified ketones together with chiral cyclic secondary amines as catalysts.252 L-proline and 5,5-dimethylthiazolidinium-4-carboxylate (DMTC) were found to be the most powerful amino acid catalysts for the reaction of both acyclic and cyclic ketones as aldol donors with aromatic and aliphatic aldehydes to afford the corresponding... 

Free-radical additions of trichlorosilane to acetylenes initiated by benzoyl peroxide were stereospecific trans additions, giving only cis adducts. The same workers observed that tri-n -butyl amine also catalyzed addition of trichlorosilane to phenylacetylene but gave a mixture of cis- and trans -l-phenyl-2-trichlorosilylethene, 1,1-phenyltrichlorosilylethene, and 1-phenyl-l,2-bistrichlorosilylethane (54). No stereospecificity was observable with the amine as catalyst. 

The reaction of 2-aminobenzothiazoles and chlorocarbonylsulfenyl chloride, with or without amines as catalyst, provides a new entry to the synthesis of [l,2,4]thiadiazolo[3,4- ]benzothiazol-3(3/7)-ones <1997H(45)1579> in modest yields. In the best example, 6-methyl-2-aminobenzothiazole 413 gives the target molecule 414 in 40% yield without adding any base (Equation 86). 

Direct phosgenation can also be carried out in aqueous sodium hydroxide rapidly stirred with methylene chloride containing a tertiary amine as catalyst. 

Epoxides can react with alcohols via acidic or basic catalysed reaction mechanisms. However, since both strong acids and bases will degrade the cell wall polymers of wood, the reaction is usually catalysed via the use of amines, which are more strongly nucleophilic than the OH group. For example, whereas the production of epoxy-phenolic resins requires temperatures in the region of 180-205 °C, reaction between epoxides and primary or secondary amines takes place at 15 °C (Turner, 1967). Reaction of epoxides with wood often involves the use of tertiary amines as catalysts (Sherman etal., 1980). The sapwood is more reactive towards epoxides than heartwood (Ahmad and Harun, 1992). 

Chiral Anions Using Secondary and Primary Amines as Catalysts. 330... 

The phosphine-catalysed reaction between an aldehyde and an acrylate yielding p-hydroxy-ot-methylene structures was first described by Morita et al. in 1968 (Scheme 37) [85]. In 1972, Baylis and Hillman [86] used a tertiary amine as catalyst and improved the yield of this reaction. 

The base-catalyzed rearrangement of oxadiazolylureas 184 into ben-zoylamino-l,2,4-triazolin-5-ones 185 has been mechanistically examined by using amines as catalysts in acetonitrile and benzene, and borate buffers at various pS in dioxan-water [90JCS(P2)1289]. For the piperidine-... 

Secondary amines as catalysts via R2C=NR2. Stability of five and six membered rings. Instability of four membered rings. 

Reeves and Hilbrich288 have reported the catalysis by pyridines of benzyl ketone alkylation they are less efficient than aliphatic trialkylamines. Reeves and White289 have also described the reaction of alkyl bromides with sodium cyanide, where pyrazine is a better catalyst (99% yield) compared to pyridine (12% yield). Isakawa et al.289 have also carried out addition of dichloro-carbene to cyclohexene under biphasic conditions, using heterocyclic amines as catalysts (e.g., iV-butylpiperidine gives 76% yield). 

In practice, epoxy-amine reactions in carbon fiber prepregs, and epoxyphenol reactions in molding compounds, are often accelerated by the addition of a Lewis acid (typically a BF3 - amine complex) or a Lewis base (often a tertiary amine), as catalysts. ... 

A A /V /V -Tetramethylelhylcncdiaminc (TMEDA) as catalyst of the Morita-Baylis-Hillman reaction has been found to be more efficient than DABCO in aqueous media.146 1-Methylimidazole 3-/V-oxide promotes the Morita-Baylis-Hillman reaction of various activated aldehydes with ,/i-unsaturated ketones and esters CH2= CHCOR (R = Me, OMe) in solvent-free systems.147 In another study, the Morita-Baylis-Hillman reaction has been successfully performed under aqueous acidic conditions at pH 1, using a range of substrates and tertiary amines as catalysts.148... 

In contrast, sample 70bs2, which was synthesized using the amine catalysts [49] (see Table 3.4), is composed of particles with an average particle diameter, D = 100 nm. This fact indicates that the sphere-packing microstructure was broken [49], The rest of the materials synthesized using the amine as catalysts have microstructures similar to those reported for sample 70bs2 [49],... 

The dimethyl perfluorodiimidate was obtained by addition of methanol onto the corresponding dinitrile, under nitrogen, with a tertiary amine as catalyst. 

Polyurethane is also used as a foam, mostly in sheet form as an underlay or middle layer for example in fruit bins. The following starting materials for polyurethane foam can be used polyester with hydroxyl end groups made from adipic acid, diethylene glycol, trimethylol propane as well as polyether based on ethylene oxide and/or propylene oxide with free hydroxyl groups in combination with 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. Stabilizers, dispersants and amines (as catalysts in amounts up to 1.2 %) can be used. 

Heterocyclic tertiary amines as catalysts for the reaction of activated vinyl carbanions with aldehydes 88T4653. 

France S, Guerin DJ, Miller SJ, Leckta T. Nucleophilic chiral amines as catalysts in asymmetric synthesis. Chem. Rev. 2003 103 2985-3012. 

Hann-Lapworth mechanism with tertiary amines as catalysts ... 

Hydrolytically stable organotin compounds are also being prepared with sulfonic acids. " These di-alkyltin and trialkyltin sulfonates can be used in combination with t -amines as catalysts in the preparation of polyurethane foams. 

Nucleophilic chiral cyclic amines as catalysts in asymmetric synthesis 03CRV2985. 

The nucleophilic addition on substituted ketenes is a well-known method to generate a prochiral enolate that can be further protonated by a chiral source of proton. Metallic nucleophiles are used under anhydrous conditions therefore, the optically pure source of proton must be added then (often in a stoichiometric amount) to control the protonation. In the case of a protic nucleophile, an alcohol, a thiol, or an amine, the chiral inductor is usually present at the beginning of the reaction since it also catalyzes the addition of the heteroatomic nucleophile before mediating the enantioselective protonation (Scheme 7.5). The use of a chiral tertiary amine as catalyst generates a zwitterionic intermediate B by nucleophilic addition on ketene A, followed by a rapid diastereoselective protonation of the enolate to acylammonium C, and then the release of the catalyst via its substitution by the nucleophile ends this reaction sequence. 

It is well known that with the tertiary amines as catalysts it is impossible to obtain high molecular weight polyether chains (for example polyethers for flexible foams) but with short chain polyethers, having 1-3 alkylene oxide units, it is perfectly possible [31, 32]. 

The point of the sudden change in the PO consumption rate is the moment of total transformation of the initial amine in a trialkanolamine of lower catalytic activity. Because of the low PO polymerisation rate in the second part of the reaction, at normal polymerisation temperatures of 110-120 °C, it is practically impossible to obtain, in the presence of tertiary amines as catalysts, polyether polyols with an hydroxyl number lower than 400 mg KOH/g. 

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