Secondary amine — epoxide reaction

Fig. 22a and b. (i) Epoxide-hydroxyl and (ii) secondary amine-epoxide reactions that form (a) inter-molecular crosslinks and (b) intramolecular rings... 

To attain the requirements of an epoxy matrix utilized in filament-wound C-fiber-epoxy composites we have considered the characteristics required of the amine curing agent molecule. To ensure long gel times at 23 °C requires that the primary amine-epoxide (P.A.-E) reaction rate is considerably greater than the rate of the secondary amine-epoxide (S. A.-E) reaction, and that the S.A. reaction does not occur at low temperatures. Furthermore, to attain low 23 °Cr s and low post-cure temperatures... 

Primary and secondary amines also react with epoxides (or in situ produced episulfides )r aziridines)to /J-hydroxyamines (or /J-mercaptoamines or 1,2-diamines). The Michael type iddition of amines to activated C—C double bonds is also a useful synthetic reaction. Rnally unines react readily with. carbonyl compounds to form imines and enamines and with carbo-tylic acid chlorides or esters to give amides which can be reduced to amines with LiAlH (p. Ilf.). All these reactions are often applied in synthesis to produce polycyclic alkaloids with itrogen bridgeheads (J.W. Huffman, 1967) G. Stork, 1963 S.S. Klioze, 1975). 

Primary cycloaUphatic amines react with phosgene to form isocyanates. Reaction of isocyanates with primary and secondary amines forms ureas. Dehydration of ureas or dehydrosulfuri2ation of thioureas results in carhodiimides. The nucleophilicity that deterrnines rapid amine reactivity with acid chlorides and isocyanates also promotes epoxide ring opening to form hydroxyalkyl- and dihydroxyalkylaniines. Michael addition to acrylonitrile yields stable cyanoethylcycloalkylarnines. 

The reaction between epoxides and ammonia is a general and useful method for the preparation of P-hydroxyamines. " Ammonia gives largely the primary amine, but also some secondary and tertiary amines. The useful solvents, the ethanolamines, are prepared by this reaction. For another way of accomplishing this conversion, see 10-54. The reaction can be catalyzed with Yb(OTf)3 and in the presence of a-BINOL is l,l -bi-2-naphthol derivative gives amino alcohols with high asymmetric induction. A variation used Yb(OTf)3 at lOkbar or at ambient pressure. Lithium triflate can also be used. Primary and secondary amines give, respectively, secondary and tertiary amines, for example. 

The reaction of the epoxide with a thiol group yields a thioether linkage, whereas reaction with a hydroxyl gives an ether and reaction with an amine results in a secondary amine bond. The relative reactivity of an epoxy group is thiol > amine > hydroxyl, and this is reflected by... 

Porath, 1974). B/s-oxirane compounds also can be used to introduce epoxide groups into soluble dextran polymers in much the same manner (Boldicke et al., 1988 Bocher et al., 1992). The epoxide group reacts with nucleophiles in a ring-opening process to form a stable covalent linkage. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary amine, thioether, or ether bonds, respectively (Chapter 2, Section 1.7). 

To date, the most frequently used ligand for combinatorial approaches to catalyst development have been imine-type ligands. From a synthetic point of view this is logical, since imines are readily accessible from the reaction of aldehydes with primary or secondary amines. Since there are large numbers of aldehydes and amines that are commercially available the synthesis of a variety of imine ligands with different electronic and steric properties is easily achieved. Additionally, catalysts based on imine ligands are useful in a number of different catalytic processes. Libraries of imine ligands have been used in catalysts of the Strecker reaction, the aza-Diels-Alder reaction, diethylzinc addition, epoxidation, carbene insertions, and alkene polymerizations. 

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). 

In conjunction with the chiral anion TRIP (156) (10 mol%), diamine 157 (10 mol%) can be used in the catalytic asymmetric epoxidation of a,p-unsaturated ketones (>90% ee) [196], while the secondary amine 158 (10 mol%) can be used for the epoxidation of both di- and trisubstituted a,P-unsaturated aldehydes (92-98% ee) (Fig. 15) [211], The facile nature of these reactions, using commercially available peroxides as the stoichiometric oxidant, together with the synthetic utility of the epoxide products suggests application in target oriented synthesis. 

In the presence of oxygen the hydroamination products can not be obtained. Instead - especially with secondary amines or diamines - dehydrogenated di- and polyadducts are formed [79]. By reaction of morpholine or piperidine in air-saturated benzene solution the bisadduct, tetraadduct epoxide and the dimer shown in Figure 3.8 could be isolated and characterized. A defined 1,4-addition pattern is found in all these products. 

Figure 2.8, is generated, presenting peaks correspondent to functional groups, such as epoxide, primary and secondary amines, and hydroxyl. The values of the absorption bands for these groups can be found in the papers referenced earlier. The basic principle of all these methods is the comparison between the spectrum of reference substances and spectra of the reactants and products of a curing reaction subjected to radiation. A qualitative and quantitative identification of the components is then possible. 

The curing rates are somewhat faster. The aziridines do not react with the secondary amines formed during the cure as the epoxides react with the hydroxyl groups. Hence, side reactions are avoided. The difficulties in producing di- and trifunctional materials of high purity have hindered the wide acceptance of aziridines except in speciality formulations. 

The reaction of epoxides with, primary or secondary amines involves the following overall reactions55 ... 

These compounds can initiate anionic polymerisation of epoxides, and when R, = H the secondary amine can react by addition to an epoxide group. Farkas and Strohm 64> have studied the reaction of 2-ethyl-4-methyl imidazole with phenyl glycidyl ether and BADGE resin using chemical analysis and proton NMR spectroscopy. They found that the imidazole readily forms adducts with epoxide of 1 1 and 1 2 molecular ratio ... 

The interpretation of the kinetics is based on the mechanisms proposed by Schechter et al.55) and Smith 57), for the reaction of secondary amines with epoxides, extended to include the primary amine reaction. The rate-determining step is assumed to be the reaction of amine, epoxide and hydroxyl or other proton-donor species, HX, to form a termolecular complex, Eq. (3-13). The proposed reaction scheme is ... 

A kinetic model which includes both amine-epoxide and hydroxyl-epoxide addition reactions, with hydroxyl autocatalysis has been proposed by Zukas 103,104). The starting point was an expression for the rate of consumption of epoxide by reaction with primary or secondary amine and hydroxyl groups... 

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