For anhydrides

Values in parentheses in the columns for Methyl, Ethyl, and Phenyl Esters and for Anhydrides and Nitriles are M.ps. 

Sodium acetate reacts with carbon dioxide in aqueous solution to produce acetic anhydride and sodium bicarbonate (49). Under suitable conditions, the sodium bicarbonate precipitates and can be removed by centrifugal separation. Presumably, the cold water solution can be extracted with an organic solvent, eg, chloroform or ethyl acetate, to furnish acetic anhydride. The half-life of aqueous acetic anhydride at 19°C is said to be no more than 1 h (2) and some other data suggests a 6 min half-life at 20°C (50). The free energy of acetic anhydride hydrolysis is given as —65.7 kJ/mol (—15.7 kcal/mol) (51) in water. In wet chloroform, an extractant for anhydride, the free energy of hydrolysis is strangely much lower, —50.0 kJ/mol (—12.0 kcal/mol) (51). Half-life of anhydride in moist chloroform maybe as much as 120 min. Ethyl acetate, chloroform, isooctane, and / -octane may have promise for extraction of acetic anhydride. Benzene extracts acetic anhydride from acetic acid—water solutions (52). 

Argininosuccinic anhydride [28643-94-9 M 272,3, [ct] -10" (H2O for anhydride formed at neutral pH), Crystd from water by adding two volumes of EtOH. An isomeric anhydride is formed if the free acid is allowed to stand at acid pH. In soln, the mixture of anhydrides and free acid is formed [see above entry]. 

Tanaka and Kakiuchi (6) proposed catalyst activation via a hydrogen donor such as an alcohol as a refinement to the mechanism discussed by Fischer (7) for anhydride cured epoxies in the presence of a tertiary amine. The basic catalyst eliminates esterification reactions (8). Shechter and Wynstra ( ) further observed that at reaction conditions BDMA does not produce a homopolymerization of oxiranes. 

Another potential site of reactivity for anhydrides in protein molecules is modification of any attached carbohydrate chains. In addition to amino group modification in the polypeptide chain, glycoproteins may be modified at their polysaccharide hydroxyl groups to form ester derivatives. Esterification of carbohydrates by acetic anhydride, especially cellulose, is a major industrial application for this compound. In aqueous solutions, however, esterification may be a minor product, since the oxygen of water is about as strong a nucleophile as the hydroxyls of sugar residues. 

Another potential site of reactivity for anhydrides in protein molecules is modification of any attached carbohydrate chains. In addition to amino group modification in the polypeptide chain, glycoproteins may be modified at their polysaccharide hydroxyl groups to form esterified... 

Spontaneous hydrolyses of carboxylic anhydrides, diaryl carbonates and aryl chloroformates are faster in cationic than in anionic micelles, regardless of the nature of the counteranion in the cetyltrimethylammonium micelle (Al-Lohedan et al., 1982b Bunton et al., 1984). This charge effect does not seem to be related to substrate hydrophobicity, although the extent of micellar inhibition (relative to reaction in water) is clearly dependent upon substrate hydrophobicity for anhydride hydrolyses. 

A.1 Equilibrium data for anhydride formation 225, A.2 Intramolecular nucleophilic catalysis of ester hydrolysis 226, A.3 Intramolecular nucleophilic catalysis of amide... 

Comparison of kinetic and thermodynamic EM s for anhydride-forming reactions"... 

A. 1 Equilibrium data for anhydride formation from succinic, maleic and phthalic acidsa... 

Not applicable for anhydrides because they are readily hydrolyzed by water forming the corresponding acid. Nevertheless, experimental methods for estimation of this parameter for hydrolysis products of anhydrides are lacking in the documented literature. Given that the hydrolysis product (acetic acid) is completely miscible with water in all proportions suggests its adsorption to soil will be nominal (Lyman et al., 1982). 

This break on either side is important for anhydrides with different R groups. The cleavc e of the N-R bond is important for amides with N-substituted alkyl groups. A primciry cimide usually has a strong peak at m/e 44, which corresponds to [0=C=NH2] ... 

Reactions with anhydrides and acid chlorides are more rapid and can occur in an essentially nonreversible fashion. But, anhydrides and acid chlorides are considered high-energy reactants since they often involve additional energy-requiring steps in their production, and are thus less suitable for large-scale production of materials. The activity energies for direct esterification and transesterification are on the order of 30 kcal/mol (120 kJ/mol) while the activation energies for anhydride and acid chloride reaction with alcohols are on the order of 15-20 kcal/mol (60-80 kJ/mol). 

Baddiley and coworkers8 speculated that the threitols would be more resistant to anhydride formation than erythritol, because their secondary hydroxyl groups are trnns-disposed. It is of interest that Klosterman and Smith,8 using somewhat more vigorous conditions, had found earlier, that, for anhydride formation, a lower temperature and shorter heating period could be used for erythritol than for threitol, thus lending support to this speculation. 

This method allows for the use of acids as a replacement for anhydrides. 

The catalytic effect has been explained in terms of the activation of the anhydride by interaction with the amine to give a zwitterionic intermediate (47 Scheme 10) (B-68MI11501). Imidazoles have also been suggested as accelerators for anhydride cures (68USP3394105). A review of the patent literature (B-77MI11502) shows that several heterocyclic compounds are of interest as curatives for epoxy resins. 

Thus, it is assumed that foods containing free fructose which have, or are in, an environment for anhydride formation will lose sweetness. 

Table 15 shows the compressive data for anhydride cured foams containing 5 wt% of several silanes. In all cases the use of the silanes resulted in an increase in compressive strength and strain to failure, although in almost every case this was accompanied by a fall in the compressive modulus, i.e. the foams were less stiff . 

Figure 7 shows the family of curves for anhydride cured foams containing 5 wt% of various silanes and it can be seen that although every silane improved the energy absorbing efficiency to a marked extent, the APES foam was the most efficient, followed closely by MPS and AAMS. Figure 8 shows similar data for the polyamide cured epoxide foams, from which it can be seen that the MPS foam was the most efficient. In these foams the flat response only held up to 25-30% strain. 

Acid chlorides are converted directly to the corresponding anilides by reaction with aniline, as described in Section 9.6.15, p. 1261. For anhydrides, heat a mixture of 1 g of the anhydride and 1 g of aniline in a boiling water bath for 5 minutes, add 5 ml of water, boil and cool. Crystallise the resulting product from water or from aqueous ethanol. 

Since, generally, H0x > HD, HL is negative, which means that TOL is a decreasing function of temperature, as systematically observed (see, e.g., Lehuy et al., 1991, for anhydride-cured epoxies). 

These compounds do not readily react with epoxy resins except in the presence of water, alcohol, or some other base, called an accelerator. Tertiary amines, metallic salts, and imidazoles often act as accelerators for anhydride cured epoxy systems. The reaction between acid anhydride and epoxy resins is illustrated in Fig. 5.7. 

Anhydrides are hygroscopic materials and should not be allowed to remain exposed to the atmosphere for extended periods. Absorption of moisture from the air or from fillers causes hydrolysis of the anhydride to the acid. When used to cure epoxy resins, this moisture absorption results in variable pot life, reduced thermal resistance, and other problems. As a result, drying of fillers is particularly recommended for anhydride systems. 

Benzyldimethylamine (BDMA) is another tertiary amine that can be used as either a sole catalyst or an accelerator with other curing agents. It is used with DGEBA epoxy resins at 6 to 10 pph. The pot life is generally 1 to 4 h, and the cure will be complete in about 6 days at room temperature. When used by itself, BDMA can provide epoxy adhesive formulations with high-temperature resistance (Chap. 15). However, BDMA is mostly used as an accelerator for anhydride and dicyandiamide cured epoxy resins. 

If present, these modify the functional group(s), e.g., in 3-amino-2-chloro-2-butenoic acid, ethyl ester, hydrochloride. Modifications are used for anhydrides, esters, and salts of acids, oxides, sulfides, and selenides of ring systems containing P and As, hydrazones, and oximes of carbonyl compounds, salts of amines, etc. 

Catalysis of the synthesis of benzoic anhydride and the hydrolysis of benzoyl chloride, diphenyl phosphorochloridate (DPPC), and benzoic isobutyric anhydride in dichloromethane-water suspensions by water-insoluble silanes and siloxanes, 3- and 4-trimethylsilylpyridine 1-oxide (3b and 3c, respectively), 1,3-bis(l-oxypyridin-3-yl)-l,1,3,3-tetramethyldisiloxane (4), and poly[methyl(l-oxypyridin-3-yl)-siloxane] (5) was compared with catalysis in the same systems by water-soluble pyridine 1-oxide (3a) and poly(4-vinylpyridine 1-oxide) (6). All catalysts were effective for anhydride synthesis and promoted the disproportionation of benzoic isobutyric anhydride. Hydrolysis of benzoyl chloride gave benzoic anhydride in high yield ( 80%) for all catalysts except 3a, which gave mixtures of anhydride (52%) and benzoic acid (39%). The order of catalytic activity for DPPC hydrolysis was 5 > 4 > 3b > 3a > 3c > 6. The results suggest that hydrophobic binding between catalyst and lipophilic substrate plays an important role in these processes. 

Note The frequencies given for the C=0 stretching vibrations for anhydrides, acid chlorides, esters, lactones, aldehydes, ketones, carboxylic acids and amides refer to the open chain or unstrained functional group in a nonconjugated system. If the carbonyl group is conjugated with a double bond or an aromatic ring, the frequency is 30 cm less. If it is... 

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