Tertiary amines as catalyst

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). 

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). 

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. 

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... 

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

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

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

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. 

In conclusion, by using low hindered tertiary amines as catalysts for PO polymerisation, higher reaction rates and a low number of side reactions are obtained, at lower polymerisation temperatures (80-90 °C), where the strong base, quaternary ammonium alcoholate is stable and the predominant catalytic species. 

Of course for rigid polyether polyol synthesis in the presence of tertiary amines as catalysts, the purification step and sometimes filtration are eliminated, the fabrication process being shorter and simpler. 

Of course, by using a low steric hindrance tertiary amine as catalyst or by neutralisation with formic acid [43] or with hydroxyacids [44], the purification step is avoided, and the fabrication process is simpler, more productive and the necessary equipment simpler. 

The technological flow for the rigid polyether polyols fabrication with KOH as catalyst and with tertiary amines as catalysts are presented in Figures 13.5 and 13.6, respectively. 

The commercial practice proved that many customers prefer a neutral polyol, in order not to change the formulations and to have the possibility of making a continuous production with polyether polyols from different polyether polyols producers, without major intervention in the composition of the polyols formulated. If neutral polyols are desired, the polyether polyols synthesised with tertiary amines as catalysts are neutralised with acidic substances, such as - phthalic anhydride, formic acid or propoxylated phosphoric acid. 

A third process of solid bisphenol A alkoxylation is to use a suspension of solid bisphenol A in final polyether polyol (40-60% bisphenol A and 60-40% liquid polyether diol). This suspension, in the presence of a tertiary amine as catalyst, is ethoxylated at 80-95 °C, with 8-9 mols of EO/mol of bisphenol A. At the end of the reaction, all the solid bisphenol A was totally transformed into liquid polyether diols [30]. The resulting polyether diols are used successfully for production of urethane-isocyanuric foams with very good physico-mechanical properties and intrinsic fire resistance. 

By propoxylation of the resulting polyols (trimethylolisocyanurate and the Mannich base (15.44), in the presence of a tertiary amine as catalyst (for example dimethylaminoethanol) new heterocyclic polyols for rigid PU foams with a triazinic structure are obtained (reactions 15.45 and 15.46). 

An analogous reaction accurs with evolution of nitrogen, when 5-(substi-tuted)amino-1,2,3,4-thiatriazoles react with isocyanate esters at room temperature, preferably in the presence of tertiary amines as catalysts. Addition of a second molecule of isocyanate tends to produce the corresponding ureas (e.g 66).78... 

The situation changes drastically if long-chain oxidants are appMed. One example of a successful regioselective oxidation of a nonactivated carbon atom comes from the use of long-chain tertiary amines as catalysts. They are first oxidized to an aminoxide with hydrogen peroxide in the presence of iron(II) salts. These radical-type oxidants to form molecular complexes with long-chain alcohols... 

Typically, bismaleimides are synthesized by reacting a diamine with maleic anhydride in two steps [277,278]. In the first one a bismaleamic acid is formed in a fast, exothermic reaction, that is carried out at room temperature. The second step consist of the imidization of the maleamic acid, usually by chemical means, with acetic anhydride in the presence of a small amount of basic sodium acetate. This step is carried out at moderate temperature to avoid premature polymerization of the double bonds. The use or tertiary amines as catalyst is also possible but the obtained product is less pure than in the case of sodium acetate. In fact, this effect has been used to prepare bismaleimides with a lower melting point, and consequently with a wider processing window [279]. 

With respect to IPDI, it should be noted that with DBTDL as catalyst the secondary isocyanate is approximately 10-20 times more reactive than the primary isocyanate. With a tertiary amine as catalyst, however, the primary isocyanate is about five times more reactive than the secondary isocyanate. 

Two separate series of experiments were carried out in order to study the reactivity of EPR-g-SA towards low Mw diols with or without the addition of a tertiary amine as catalyst, and the reactivity of EPR-g-SA towards a long-chain hydroxyl-terminated polybutadiene (HTPB). For both of them, the same experimental procedure was followed to ensure an intimate mixing of the reactants, they were all dissolved in a common solvent at room temperature and in a certain stoichiometric amount (in solution, the kinetics of esterification is very slow, thus the degree of reaction is negligible). Subsequently, the solvent is quickly removed by evaporation under vacuum at room temperature directly onto KBr disks to obtain a film which is used for IR analysis. 

Good yields of Pb(C2Hs)4 are obtained with alloys that have a high Na content, such as PbNa4, when they are allowed to react with C2H5Br or C2H5I at 20 to 35 C in the presence of water and pyridine or a secondary or tertiary amine as catalyst [23, 26]. Other reactions of lead-sodium alloys and ethyl halides in the presence of water have been described in early patents [14, 21, 22, 32, 33, 39, 41 to 43, 190] and also in the presence of alcohol [22, 42, 43, 51, 52], ether [52], amines [21], pyridine [39, 190], other protic compounds [30, 43, 130, 156, 157], or with a mixture of such additives [21, 22, 39, 42, 43, 51]. This so-called hydrous reaction was used for a short time in the 1920 s for the commercial manufacture of Pb(C2Hs)4 [583]. 

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