Anhydrides reaction mechanism

Homogeneous catalysts. With a homogeneous catalyst, the reaction proceeds entirely in the vapor or liquid phase. The catalyst may modify the reaction mechanism by participation in the reaction but is regenerated in a subsequent step. The catalyst is then free to promote further reaction. An example of such a homogeneous catalytic reaction is the production of acetic anhydride. In the first stage of the process, acetic acid is pyrolyzed to ketene in the gas phase at TOO C ... 

The first anhydride plant in actual operation using methyl acetate carbonylation was at Kingsport, Tennessee (41). A general description has been given (42) indicating that about 900 tons of coal are processed daily in Texaco gasifiers. Carbon monoxide is used to make 227,000 t/yr of anhydride from 177,000 t/yr of methyl acetate 166,000 t/yr of methanol is generated. Infrared spectroscopy has been used to foUow the apparent reaction mechanism (43). 

As shown in Figure 16.10, this reaction mechanism involves nucleophilic attack by —SH on the substrate glyceraldehyde-3-P to form a covalent acylcysteine (or hemithioaeetal) intermediate. Hydride transfer to NAD generates a thioester intermediate. Nucleophilic attack by phosphate yields the desired mixed carboxylic-phosphoric anhydride product, 1,3-bisphosphoglycerate. Several examples of covalent catalysis will be discussed in detail in later chapters. 

The reaction mechanism involves deprotonation of the carboxylic anhydride 2 to give anion 4, which then adds to aldehyde 1. If the anhydride used bears two a-hydrogens, a dehydration takes place already during workup a /3-hydroxy carboxylic acid will then not be isolated as product ... 

Anthraquinone is widely use in the manufacture of a range of dyes. Two possible routes for manufacturing anthraquinone are (1) from the reaction of 1,4-naphthoquinone with butadiene and (2) reaction of benzene with phthalic anhydride. Describe mechanisms for both these reactions and identify likely reaction conditions and any other reagents required. Compare the atom economy of the two routes. Identify three factors for each route that may influence the commercial viability. 

The advantages of the phthalonitrile process are compromised by the fact that phthalonitrile is not only much more costly than phthalic anhydride but also less easily available. In view of the intermediates which have been found so far, and in conjunction with a study of the thermal course of the reaction using differential scanning calorimetry a reaction mechanism has been proposed for the phthalonitrile route which may be visualized as follows [11] ... 

This process is similar to the formation of an ester by the action of an acid anhydride on an alcohol (described in the earlier section Acid anhydride plus an alcohol ). Half the acid anhydride forms the amide the other half is a leaving group. Ammonia, primary amines, and secondary amines react to produce amides. Figure 12-27 shows the industrial preparation of phenacetin by the reaction of an amine with an acid anhydride. The mechanism for this reaction is similar to the mechanism for the reaction of an acid chloride with an amine (refer to Figure 12-26). 

Structurally similar photochromic maleic anhydride derivatives 177 with a similar reaction mechanism were prepared by Irie (05CL64) by a one-pot synthesis from 2-methoxybenzothiophene, oxalyl chloride, and pentene-3-carboxylic acid (3-pentenoic acid) in dichloromethane in the presence of triethylamine at 5°C for 2 h according to Scheme 54. 

However, the use of techniques which analyze both the short and the long range orders of the VPO materials, like RED of X-Rays (2 ), and W MAS-NMR (3,4 ), showed the possible participation of some V (V) structures to the reaction. Previously, there has been some ambiguity insofar as these structures should be a consequence of the reoxidation of the starting VOHPO4, 0.5 H2O precursor or of the basic (VO)2P207 matrix and hence do not intervene directly in the reaction mechanism of butane oxidation to maleic anhydride. The possible role of a limited amount of V(V) sites to control the selectivity to maleic anhydride was previously postulated (5). 

With this purpose, several different types of solid acid catalysts have been investigated for the acylation of aromatics, but the best performances have been obtained with medium-pore and large-pore zeolites (3-9). In general, however, the use of acylating agents other then halides, e.g., anhydrides or acids, is limited to the transformation of aromatic substrates highly activated towards electrophilic substitution. In a previous work (10), we investigated the benzoylation of resorcinol (1,3-dihydroxybenzene), catalyzed by acid clays. It was found that the reaction mechanism consists of the direct 0-benzoylation with formation of resorcinol monobenzoate, while no primary formation of the product of C-benzoylation (2,4-dihydroxybenzophenone) occurred. The latter product formed exclusively by... 

In trying to formulate a reaction mechanism for the catalysis, the well known reaction of aluminum alcoholates with carboxylic anhydrides was used as a basis (14). For example, phthalic anhydride, maleic anhydrides, and carbon dioxide, will react so that the acid anhydride pushes itself between the metal atom and the alkoxy groups, thus separating them. This results in forming neutral aluminum salts of the monoalkyl carboxylic acids. It is possible, of course, for the conversion to proceed incompletely, having two alkoxy groups bound to the aluminum, thus having only 1 mole of acid anhvdride react on 1 mole of aluminum alcoholate. 

Catalysis of the hydrolysis of acetic anhydride by acetate ion cannot be explained in this way, since nucleophilic displacement simply generates another molecule of acetic anhydride. The mechanism of this reaction is presumed to be general base catalysis, usually written as... 

Iridium complexes in the presence of iodide also catalyze the carbonylation of methyl acetate to acetic anhydride (equation 69). The reaction mechanism is similar to that of Scheme 33. The ester reacts with HI to give methyl iodide which is carbonylated as in Scheme 33 to acetyl iodide. This reacts with acetic acid to give the anhydride.429 430... 

In the system epoxide (epoxy resin) — anhydride, we can thus expect the presence of anhydride, epoxy- and proton donor groups. In their study of the reaction mechanism, Fisch and Hofmann 20 22-24) proposed a sequence of reactions leading to the crosslinking of epoxy resins or to the formation of linear polyesters. The first step is the reaction of the anhydride with hydroxyl groups giving a monoester (Eq.(l))... 

Figure 4-5. Reaction mechanism for the derivatization followed by reductive cleavage based on Lu and Ralph (1997). Reaction of the lignin with acetylbromide (AcBr) results in the acetylation of the y-carbon, while the a-carbon is brominated. Zinc (Zn) catalyzes the cleavage of the ether bond between the P-carbon of one residue and the 0-4 position of the adjacent residue. The resulting monomer is acetylated with acetic anhydride (Ac20) and pyridine (Py). R can be a proton or an aryl group. In H-residues R3 and R5 are protons, in G-residues R3 is a methoxyl group and R5 is a proton, whereas in S-residues both R3 and R5 are methoxyl groups. The wavy bonds indicate that both the S- and R- (4.26, 4.27) or E- and Z-stereo-isomers (4.28, 4.29) are present.

Monoetherification of polyols.12 Monobenzylation and monoallylation of polyols can be conducted conveniently under mild conditions by conversion to the stannylene derivative (dimeric) by di-n-butyltin oxide (5, 189 9, 141). The stannylene is then treated with benzyl bromide or allyl bromide and tetra-n-butylammonium iodide (1 equiv.) in benzene. The same conditions can be used to prepare monomethoxymethyl ethers. Quaternary ammonium bromides are less efficient catalysts than the iodides. These salts also accelerate reaction of stannylenes with acid anhydrides. The mechanism for this activation is not clear it may involve coordination of I" to tin. 

Figure 5.3 Reaction mechanism of the strictly alternating copolymerization of phenyl glycidyl ether (PGE, 2) and phthalic anhydride (PA, 3) initiated by imidazoles (la-c). (Leukel et al., 1996. Copyright 2001. Reprinted by permission ofWiley-VCH)...

Industrial research in this area is devoted mainly to the synthesis of Pc or PcM (M = Cu, Ni, Fe, Al, etc.) starting from urea and phthalic anhydride (or its derivatives) as the most cheap precursors. A survey of the literature shows that most of the articles and patents (among them Refs. 40 49) in the phthalocyanine area during the last 15 years are devoted to searching for the optimal conditions for Pc or PcM (M = Cu, Fe, Al, etc.) preparation, as well as the study and applications of different phthalocyanine modifications [50-56], synthesis of various Pc-substituted derivatives [57 66], study of reaction mechanisms of Pc formation [9,10,18,19,29,30], and much more relevant information generalized in a recent book [67]. 

The first attempt to establish the mechanisms of the anomerizations was published by Bonner.79 An extensive study was made of the anomerizations of the D-glucopyranose pentaacetates in mixtures of acetic anhydride and acetic acid in the presence of sulfuric acid. The rate of reaction was found to be greatest in pure acetic anhydride. The anomerizations were shown to be inversions specific for the anomeric center. The data did not allow definite conclusions regarding the reaction mechanisms. Nevertheless, a mechanism was proposed, for both the forward and reverse reactions, which appeared the most attractive of those which could be postulated to account for the experimental facts that the anomerization... 

Solvent effect on rate constants. In this section, the rate constant will be predicted qualitatively in CO2 for the Diels-Alder cycloaddition of isoprene and maleic anhydride, a reaction which has been well-characterized in the liquid state (23,24). In a previous paper, we used E data for phenol blue in ethylene to predict the rate constant of the Menschutkin reaction of tripropylamine and methyliodide (19). The reaction mechanisms are quite different, yet the solvent effect on the rate constant of both reactions can be correlated with E of phenol blue in liquid solvents. The dipole moment increases in the Menschutkin reaction going from the reactant state to the transition state and in phenol blue during electronic excitation, so that the two phenomena are correlated. In the above Diels-Alder reaction, the reaction coordinate is isopolar with a negative activation volume (8,23),... 

Maleic anhydride reacts with cyclopenta-1,3-diene in a Diels-Alder reaction. Since there is a plane of symmetry, the reaction can lead to two achiral compounds, which are diastereomers of each other, containing an endo- or exo-oriented dicarboxylic anhydride group. These differ in absolute and relative configuration at the bond shared by both rings. Under normal conditions the Diels-Alder reaction proceeds stereospecifically to yield preferentially the endo product. Note that in the tricyclic product no trans fusion in the ring system is possible as a consequence of the reaction mechanism. Subsequent reduction of the products therefore affords two diols, which are also diastereomers of each other. These may be separated by chromatography on an achiral stationary phase. 

The polyaddition reaction is the most commonly used type of reaction for the cure of epoxy resins. The curing agents used in this type of reaction have an active hydrogen compound, and they include amines, amides, and mercaptans. With this reaction mechanism, the most important curing agents for adhesives are primary and secondary amines containing at least three active hydrogen atoms and various di- or polyfunctional carboxylic acids and their anhydrides. 

The reaction of anhydrides with epoxy groups is complex, with several competing reactions capable of taking place. The most significant reaction mechanisms are as follows ... 

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