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Acetic anhydride solvent system

Others have also looked at the kinetic characteristics of the solution homopolymerization of MA, using benzene, dioxane, and acetic anhydride solvents with BPO initiator. In dioxane, polymerization rates are proportional to initiator concentration to the power, supporting a recombination mechanism for termination of the kinetic chains. Reminiscent of the y-radiation polymerization systems, an increased rate of polymerization and greater molecular weight is observed in acetic anhydride solvent. All evidence supports the assumption that acetic anhydride is not a pure solvent for the... [Pg.244]

Recently, use of LiCl/DMAc and LiCl/l,3-dimethyl-2-imidazolidinone as solvent systems for acetylation of cellulose by acetic anhydride/pyridine has been compared. A DS of 1.4 was obtained the substituent distribution in the products synthesized in both solvents was found to be the same, with reactivity order Ce > C2 > C3. Therefore, the latter solvent system does not appear to be better than the much less expensive LiCl/DMAc, at least for this reaction. It appears, however, to be especially efficient for etherification reactions [178]. It is possible, however, that the effect of cellulose aggregation is more important for its reaction with the (less reactive) halides than with acid anhydrides this being the reason for the better performance of the latter solvent system in ether formation, since it is more efficient in cellulose dissolution. [Pg.130]

As previously discussed, solvents that dissolve cellulose by derivatization may be employed for further functionahzation, e.g., esterification. Thus, cellulose has been dissolved in paraformaldehyde/DMSO and esterified, e.g., by acetic, butyric, and phthalic anhydride, as well as by unsaturated methacrylic and maleic anhydride, in the presence of pyridine, or an acetate catalyst. DS values from 0.2 to 2.0 were obtained, being higher, 2.5 for cellulose acetate. H and NMR spectroscopy have indicated that the hydroxyl group of the methy-lol chains are preferably esterified with the anhydrides. Treatment of celliflose with this solvent system, at 90 °C, with methylene diacetate or ethylene diacetate, in the presence of potassium acetate, led to cellulose acetate with a DS of 1.5. Interestingly, the reaction with acetyl chloride or activated acid is less convenient DMAc or DMF can be substituted for DMSO [215-219]. In another set of experiments, polymer with high o -celliflose content was esterified with trimethylacetic anhydride, 1,2,4-benzenetricarboylic anhydride, trimellitic anhydride, phthalic anhydride, and a pyridine catalyst. The esters were isolated after 8h of reaction at 80-100°C, or Ih at room temperature (trimellitic anhydride). These are versatile compounds with interesting elastomeric and thermoplastic properties, and can be cast as films and membranes [220]. [Pg.138]

In general, symmetrical oxo-squaraines having the same end-groups are synthesized by reacting squaric acid with two equivalents of quatemized indolenine, 2-methyl-substituted benzothiazole, benzoselenazole, pyridine, quinoline [39, 45, 46] (Fig. 4) in a mixture of 1-butanol - toluene or 1-butanol - benzene with azeotropic removal of water in presence [39, 45] or absence [47] of quinoline as a catalyst. Other reported solvent systems include 1-butanol - pyridine [48], 1-propanol - chlorobenzene, or a mixture of acetic acid with pyridine and acetic anhydride [49]. Low CH-acidic, heterocyclic compounds such as quatemized aryl-azoles and benzoxazole do not react, and the corresponding oxo-squaraines cannot be obtained using this method [23, 50]. [Pg.73]

The behavior of acetic anhydride as a solvent system indicates an ionization 201 208... [Pg.101]

Because of the reaction conditions employed (poor donor solvent, absence of nucleophilic reagents for ligand displacement) it seems certain that a ligand reaction is occurring in this system, and not acetylation of displaced ligand as is probable in the acetic acid-acetic anhydride system. [Pg.150]

Spiro-A4-sulfane 25 was found to transform into cyclic dibenzodithiazocine 47 by refluxing in the mixture of acetic anhydride and pyridine for 3 h (Equation 8) <1995CC1069>. This rearrangement can also be carried out in pyridine, acetic acid, Ac20-AcOH, pyridine—/>-dimcthy lam i nopyridine mixed solvent systems. [Pg.48]

Subsequently the alkenylglycerols can be reacted with acetic acid anhydride-pyridine, usually a 1 5 (v/v) mixture, in a sealed tube. The tube is heated at 70-80°C for 45 min and then cooled to room temperature, and the seal is carefully broken. The contents are diluted with an equal volume of water and extracted with n-hexane. Two separate extractions with n-hexane should allow complete recovery of the alkenylglycerol diacetates. The combined hexane extracts are washed with water until neutral and then dried over anhydrous Na2S04. The purity of the preparation can be determined by thin-layer chromatography on silica gel G in a solvent system of petroleum ether-diethyl ether-acetic acid (80 20 1, v/v). Again two separate plates can be run, one for spraying with TNS and the other for charring with sulfonic acid (plus heat). [Pg.116]

Over HBEA zeolites, acetylation of 2-methoxynaphthalene with acetic anhydride leads mainly to l-acetyl-2-methoxynaphthalene. However, the desired product, i.e. 2-acetyl-6-methoxynaphthalene, precursor of Naproxen is obtained at long reaction time by an intermolecular irreversible isomerization process. A very selective production of II (83%) can be obtained by acetylation of 2-methoxynaphthalene over a commercial HBEA zeolite (Si/Al = 15) at 170°C, with nitrobenzene as a solvent. With dealuminated HBEA samples (framework Si/Al ratio between 20 and 40), better results could be expected. Furthermore, preliminary experiments showed that this selective synthesis of 2-methoxynaphthalene can be carried out in a flow reactor system. [Pg.151]

NPC is ideally suited for the analysis of compounds prone to hydrolysis because it employs nonaqueous solvents for the modulation of retention. An example of the use of NPC in the analysis of a hydrolysable analyte was demonstrated by Chevalier et al. [28] for quality control of the production of benorylate, an ester of aspirin. A major issue in benorylate production is the potential formation of impurities suspected of causing allergic side effects therefore monitoring of this step is critical to quality control. The presence of acetylsalicylic anhydride prohibited the use of RPLC since it can be easily hydrolyzed in the water-containing mobile phase. However, an analytical method based on the use of normal-phase chromatography with alkylnitrile-bonded silica as the stationary phase provided an ideal solution to the analysis. Optimal selectivity was achieved with a ternary solvent system hexane-dichloromethane-methanol, containing 0.2 v/v% of acetic acid to prevent the ionization of acidic function and to deactivate the residual silanols. The method was validated and determined to be reproducible based on precision, selectivity, and repeatability. [Pg.251]

As noted, the bimolecular reduction of aromatic nitro compounds may produce azoxy compounds, azo compounds, hydrazo compounds (1,2-diaryIhydrazines), benzidines or amines (Scheme 1) depending on the reaction conditions. Zinc reduction under basic conditions generates azo compounds, whereas the use of acetic anhydride/acetic acid as the solvent system affords symmetrical azoxy compounds. Although unsymmetrical azoxy compounds are accessible in the aliphatic series, aromatic reagents yield only sym-... [Pg.364]

The reaction of oarboxylate with various substrates is an example of a system which necessitates a careful search for products. Early examples of these reactions demonstrated that direct nucleophilic attack takes place. For example, using a dilatometric method, formate was found to catalyze strongly the hydrolysis of acetic anhydride whereas propionate and butyrate slow down the reaction (Kilpatrick, 1928). These results are attributable to mixed anhydride formation with the total rate being determined by the reactivity of the mixed anhydride. The reaction of acetate with 2,4-dinitrophenyl benzoate results in the formation of an unstable mixed anhydride, as was shown in an experiment in which 0 labeled acetate was used the benzoic acid product contains 75% of the O label (Bender and Neveu, 1958). The other 25 % of the O label is presumed to be lost to acetate by solvent attack at the benzoyl carbon if direct nucleophilic interaction is the sole path. [Pg.271]


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See also in sourсe #XX -- [ Pg.101 ]




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