Side reactions tertiary amine

Open times of two-component urethanes can vary widely, depending on the level of catalyst. Reaction times can vary from 90 s to over 8 h. Dibutyltin dilaurate is the most common catalyst employed to catalyze the urethane reaction. This is normally added to the polyol side. A tertiary amine may also be added in small amounts. Tin catalysts do not catalyze the amine/isocyanate reaction very well. Acids, such as 2-ethyl hexanoic acid, may be employed to catalyze the amine/isocyanate reaction where needed. 

Allow a mixture of 0-5 g. of the tertiary amine and 0-5 ml. of colourless methyl iodide to stand for 5 minutes. If reaction has not occurred, warm under reflux for 5 minutes on a water bath and then cool in ice water. The mixture will generally set solid if it does not, scratch the sides of the tube with a glass rod. RecrystaUise the solid product from absolute alcohol, ethyl acetate, acetone, glacial acetic acid or alcohol-ether. 

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

One characteristic of this reaction that can cause problems is that secondary and tertiary amines are produced in addition to the primary amine. It has been proposed that these side reactions occur through reaction of the imine iatermediate with the product amine, followed by the loss of ammonia and further hydrogenation (10). 

The tertiary amine is formed in a similar manner from the imine and a secondary amine. This side reaction can be minimized by carrying out the hydrogenation in the presence of ammonia, which tends to shift the equiHbrium back towards the imine. When a compound with two or more nitrile groups is hydrogenated, the formation of both cycHc and acycHc secondary and tertiary amines is possible, depending on whether the side reaction is intramolecular or intermolecular. For example, for the hydrogenation of adiponitfile ... 

Whilst reaction can take place in the absence of catalysts it is more common to use such materials as tetra-alkylammonium halides and tertiary amines such as triethylenediamine. A major side reaction leads to the production of isocyanurate rings, particularly in the presence of tertiary amines. 

Catalysts such as dibutyl tin dilaurate or tertiary amines are added to promote the urethane reaction and/or subsequent moisture cure. Dimorpholine diethyl ether is particularly effective at promoting moisture cure without promoting allophanate side reactions at the application temperature (which leads to instability in the hot melt pot) [29]. 

The formation of a weakly basic tertiary amine in reaction 4.102 does not alter the titrant normality, but in the titration of an acid it may suppress the height of the titration curve on the basic side. In an extensive study of twelve quaternary ammonium titrants in non-aqueous media (mainly isopropyl alcohol), Harlow73 observed large differences in stability the presence of water had a profound stabilizing action but at the sacrifice of basic strength inert and basic solvents increased the rate of decomposition (see Fig. 4.18). 

The thermal isomerization of higher terminal alkynes also delivered some allene, from 1-hexyne and 1-heptyne, for example, some 1,2-diene was formed [30]. With an ,/l-unsaturated unit in the alkyne 9, a photochemical isomerization to 10 was successful but delivered only a low yield and 11 as a significant side-product [31]. These reactions tolerate different functional groups alcohols, ethers or, as in 12, tertiary amines and nitriles have been used (Scheme 1.5) [32, 33],... 

The hydrochloric acid is removed by the strong tertiary base, methyldibutylamine, which has a soluble hydrochloride. In B.P. s 631,549 and 652,981 it was shown that compound (II) could be prepared by the action of dimethylamine on P0C13 in chloroform containing an excess of methylbutylamine. The further reaction with water is very conveniently carried out in the same system by adding an excess of aqueous sodium hydroxide solution. The chloroform layer contains the tertiary amine and (I). The solvent and amine are stripped off leaving the product. Side reactions take place, and the commercial product also contains some triphosphoric pentadimethylamide (I A) and smaller amounts of other phosphoric amides. The compound (I A) is itself also a valuable systemic insecticide. 

More /V-acylurea is generated if tertiary amine is present because the latter removes any protons that might prevent the rearrangement (see Section 2.12). The two intramolecular reactions also occur to a greater extent when interaction between the O-acylisourea and the /V-nucleophile is impeded by the side chain of the activated residue. This means that more 2-alkoxy-5(4//)-oxazolone and /V-acylurea are generated when the activated residues are hindered (see Section 1.4). A corollary of the above is that the best way to prepare an /V-acylurea, should it be needed, is to heat... 

FIGURE 2.14 Peptide-bond formation from chlorides of A-alkoxycarbonylamino acids. N-9-Fluorenylmethoxycarbonylamino-acid chlorides.41 The base is NaHCO, Na2C03, or a tertiary amine. The reaction is carried out in a one- or two-phase system. The latter is used to try to suppress formation of the 2-alkoxy-5(4//)-oxazolone that is generated by the action of the base on the acid chloride. The method is applicable primarily to Fmoc-amino-acid derivatives that do not have acid-sensitive protecting groups on their side chains. 

BOP, PyBOP, HBTU, HATU, and so forth with an additive It has been considered essential to use an additive with these reagents because the tertiary amine required to effect the coupling promotes isomerization. Diisopropylethylamine or possibly trimethylpyridine are the bases of choice to minimize the side reaction, but the additive may increase isomerization (see Section 7.18). 

A second method of activating the acid for esterification (see Section 7.6) is as the mixed anhydride. The mixed-anhydride reaction had been employed decades ago for preparing activated esters. However, it was never adopted because of its unreliability and the modest yields obtained. The method was fine-tuned (Figure 7.12), after reliable information on the properties of mixed anhydrides was acquired (see Section 2.8). Tertiary amine is required for esterification of the mixed anhydride to occur. The method is generally applicable, except for derivatives of asparagine, glutamine, and serine with unprotected side chains. The base also prevents decomposition that occurs when the activated derivative is a Boc-amino acid (see... 

The phosphonium and carbenium salts are efficient reagents for activating and coupling A-alkoxycarbonylamino acids as well as peptide acids. However, the requirement for tertiary amine to effect the reaction has several implications. The base renders hydroxyl groups subject to acylation. Hence, the side chains of serine and threonine and any hydroxymethyl groups of a resin that have not been derivatized... 

Apart from the increased catalytic efficiency, this structure design produced two positive side effects. In contrast to monofunctional (thio)ureas, which exhibit low solubility in nonpolar solvents due to intermolecular hydrogen-bonding association, tertiary amine thioureas of type 12 revealed intramolecular hydrogen bonding between the amine group and the amide protons making these (thio)ureas soluble in nonpolar reaction media such as toluene. The analysis of the X-ray crystal-... 

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