Amines and acid anhydrides

Both amines and acid anhydrides are extensively used cross-linking agents. The resins may also be modified by reacting with other polymers containing hydroxyl or mercaptan groupings, e.g. 

In one example sequence the technology has been used to synthesize a variety of amides from amines and acid anhydrides. It is currently also being used to optimize reactions through the variations of auxiliaries and solvents and might become an interesting and more direct alternative to solid-phase synthesis. 

Properties of an amine and acid anhydride cured brominated epoxy compound LXIV (Scheme 79) which contains a cycloaliphatic ring are presented in... 

To convert the epoxy resins into cross-linked structures, it is necessary to add a curing agent. Most of the curing agents in common use can be classified into three groups tertiary amines, polyfunctional amines, and acid anhydrides. 

Diglycidyl ethers of Bisphenol A cannot be cross-linked through heating alone. Chemical cross-linking agents must be added. Most commonly used compounds are tertiary amines, polyfunctional amines, and acid anhydrides. Lewis acid, phenols, and compounds like dicyandiamide, however, are also used. 

That epoxide groups are also present in oxidized natural rubber has been demonstrated by Golub et al (1975) by the use of H NMR and NMR spectroscopy. The presence of occasional epoxide groups is not believed to have a great effect on the properties of natural rubber but it may be noted in passing that, in theory, it provides sites for cross-linking by such materials as amines and acid anhydrides which are well known as epoxide resin hardeners. At the present time the above reaction sequence is of more interest in that it provides a route for converting peroxy radicals into alkoxy radicals and is believed by some workers to play an important role in chain scission due to autoxidation. 

The predominance of one reaction over the other is greatly influenced by the catalyst system employed. Amines and acid anhydrides are extensively used as curing agents. Tertiary amine systems are often used in practice. In addition to the catalytic reactions, the epoxy resins may be cross-linked by agents that link across the epoxy molecules. These reactions may be via the epoxy ring or through the hydroxyl groups, as illustrated below. 

The diglycidyl ether of bisphenol A DGEBA is widely used as a resin in epoxide adhesives. The three principal groups of compounds that are used to cure such epoxide adhesives are aliphatic amines, aromatic amines, and acid anhydrides. Cure with aliphatic amines occurs at lower temperatures than that with aromatic amines and acid anhydrides. This temperature difference is reflected in the Tg of the cured adhesive. Also epoxides cured with aromatic amines have higher Tgs than those with aliphatic amines, as the former have less flexible molecules than the latter. This is illustrated in Table 18.5 where DAPEE and TETA are aliphatic, and DAB and DDM aromatic. 

Two molar equivalents of amine are required m the reaction with acyl chlorides and acid anhydrides one molecule of amine acts as a nucleophile the second as a Brpnsted base... 

The reactions of primary amines and maleic anhydride yield amic acids that can be dehydrated to imides, polyimides (qv), or isoimides depending on the reaction conditions (35—37). However, these products require multistep processes. Pathways with favorable economics are difficult to achieve. Amines and pyridines decompose maleic anhydride, often ia a violent reaction. Carbon dioxide [124-38-9] is a typical end product for this exothermic reaction (38). 

By contrast with tertiary amines used in catalytic quantities, primary and secondary amines or acid anhydrides may be used to bring about the cure of epoxy resins by reaction in stoichiometric proportions. A typical amine curing agent used at this level is diaminodiphenylmethane (DDM), which reacts with an individual epoxy-group in the way shown in Reaction 4.17. 

Oxidation is the first step for producing molecules with a very wide range of functional groups because oxygenated compounds are precursors to many other products. For example, alcohols may be converted to ethers, esters, alkenes, and, via nucleophilic substitution, to halogenated or amine products. Ketones and aldehydes may be used in condensation reactions to form new C-C double bonds, epoxides may be ring opened to form diols and polymers, and, finally, carboxylic acids are routinely converted to esters, amides, acid chlorides and acid anhydrides. Oxidation reactions are some of the largest scale industrial processes in synthetic chemistry, and the production of alcohols, ketones, aldehydes, epoxides and carboxylic acids is performed on a mammoth scale. For example, world production of ethylene oxide is estimated at 58 million tonnes, 2 million tonnes of adipic acid are made, mainly as a precursor in the synthesis of nylons, and 8 million tonnes of terephthalic acid are produced each year, mainly for the production of polyethylene terephthalate) [1]. 

Despite the amount of research focused on the iV-nitration of amines with nonacidic reagents, the use of conventional acidic reagents based on nitric acid and acid anhydrides has been far more extensive for the synthesis of energetic materials. 

The ionic liquid [BMIM]BF4 was found to efficiently catalyze the three-component coupling reactions of aldehydes, amines, and homophthalic anhydride under ambient conditions to give the corresponding c/ -isoquinolonic acids in excellent yields with... 

The classes of compounds which are conveniently considered together as derivatives of carboxylic acids include the carboxylic acid anhydrides, acyl chlorides, esters, and amides. In the case of simple aliphatic and aromatic acids, synthetic transformations among these derivatives are usually a straightforward matter involving such fundamental reactions as ester saponification, formation of acyl chlorides, and the reactions of amines with acid anhydrides or acyl chlorides ... 

Esters are less reactive than acid chlorides and acid anhydrides. They are converted to carboxylic acid hy acid or base hydrolysis, and to another ester by acid or base alcoholysis (transesterification). The 1°, 2° or 3° amides are obtained from esters by treatment with ammonia or 1° or 2° amines, respectively. 

Preparation of amides Ammonia and 1° and 2° amines react with acid chlorides and acid anhydrides to give 1°, 2° and 3° amides, respectively, in the presence of excess pyridine (C5H5N) or triethylamine (Et3N). In the case of acid anhydride, two molar equivalents of ammonia or amines are required. 

The most common acylating agents are the acyl chlorides and acid anhydrides of ethanoic acid and benzoic acid. The amine can be recovered from the amide by acid- or base-catalyzed hydrolysis ... 

The reaction under consideration is typified by the formation of saturated carboxylic acids from olefins, carbon monoxide, and water. Other compounds have been used in place of olefins (alkyl halides, alcohols), and besides water, a variety of compounds containing active hydrogen may be employed. Thus, alcohols, thiols, amines, and acids give rise to esters, thio-esters, amides, and acid anhydrides, respectively (15). If the olefin and the active hydrogen are part of the same molecule, three or four atoms apart, cyclizations may occur to produce lactones, lactams, imides, etc. The cyclizations are formally equivalent to carbonylations, however, and will be considered later. 

K, is nearly 100 for EDA and DETA since there is no restraint in the molecules of the curing agents q(E ) is higher and Tg is slightly elevated in Im and Sue A since the restraint is high. This is due to increasing flexibility of the main chain in the series hydrocarbon < polyether < polyester. For DGEBA resins, Tg increases in the series amine- > catalyst- > acid anhydride, for the same valne of q(E.,. 

Tetrahydroisoquinolonic acids are formed in good yields and enhanced rates from three-component coupling reactions of benzaldehydes, amines, and homophthalic anhydride. The key feature of this approach is the use of ionic liquids <03T1805>. 

Towards other singly-bonded electrophiles, the stannylamines behave as mild nucleophiles. The more reactive alkyl halides can be converted into the corresponding alkyl amines (equation 16-43 and 16-44)35, and acid anhydrides (equation 16-45)31 and acyl halides (equation 16-46)36 give the amides. 

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