Acetic anhydride method

Benzoic anhydride (carboxylic acid - acetic anhydride method). 

Anilino vinyl derivatives of thiazolium (30, R = H) or acetanilido (30, R = C0CH3), as well as formyl methylene 30b (methods E-G), give asymmetrical dyes when condensed with a methyl reactive group of another species (Scheme 42). Mesosubstituted symmetrical or unsymmet-rical thiazolocyanines are obtainable via /S-alkylmercaptovinyl thiazolium derivatives (32) (methods H and I) (Scheme 43). a or /S carbon atoms of the trimethine chain can be substituted by acetyl when a dye is treated with acetic anhydride (method L). The hydrolysis of neocyanines lead to trimethine cyanine by fractional elimination of a composant chain (method K). 

Following methods are described in Std-MethodsChemAnalysis 2A(1963), pp 455—460 Esterification with Acetic Anhydride, Method 1 Uncatalyzed Reagent. It is based on the following- reaction ... 

Marier, J. R. and Boulet, M. (1958). Direct determination of citric acid in milk with an improved pyridine-acetic anhydride method.. Dairy Sci. 41,1683-1692. 

An oxidation where this system is superior is in the reaction of caitwhydrate derivatives where it is notably better than the acetic anhydride method, maiidy due to die shorter reaction times, e.g. the preparation of the ketone (14 equation 7). ... 

Using lead acetate as a catalyst with acetyl chloride, Singh et al. (71) found a lower acetyl content than with the acetic anhydride method. They obtained much higher ASE values, however, with acetyl chloride (60-84% for acetyl chloride vs. 47% for acetic anhydride). By using a 20% lead acetate solution, the amount of free HCl released in the reaction is reduced. This very strong acid causes extensive degradation of the wood, and because of this very little work has been done in this area. 

Chemical binding. Synthesis of the aldehyde-terminated PEG (PEG-CHO) was accomplished by a mo fication of the acetic anhydride method of Harris et al.(79) All solvents, excluding acetic anhydride, were dried over molecular sieves. The formation of aldehydes was monitored at 560 nm using the Schiff reagent (79). 

According to ISO 4326, the acetic anhydride method is subject to interference from a large number of materials, including amines, amides, thiols, epoxides and some fatty acids and esters, and is not applicable to propylene oxide adducts. The phthalic anhydride method may be subject to the same constraints, but the ASTM method does not say so. 

For the acetic anhydride method, the volume of sodium hydroxide includes the 25 ml added at step 6. 

ISO 4326 1980 Nonionic surface active agents— Polyethoxylated derivatives— Determination of hydroxyl value— Acetic anhydride method. International Organization for Standardization, Geneva. 

Dehydration of carboxaldoximes is often accomplished by the acetic anhydride method as it is a convenient and low-cost reagent. Veratronitrile 1402 is prepared from veratraldoxime by dehydration with acetic anhydride in 72-78% yield according to a procedure from the year 1935 [1067]. 

The acetic anhydride method has been modified by the inclusion of potassium acetate in the reaction mixture. Under these conditions, 2-picoline and benzaldehyde give a good yield of 2-stilbazole, 3-picoline does not react, 2,6-lutidine forms the di- and some mono-stilbazolei , and 2,4,6-collidine gives the tri-stilbazole . 

Although the acetic anhydride method has frequently been preferred to the zinc chloride method because it is more convenient, the claim that it gives better yields of cleaner products is not generally true. A comparison of the three methods, zinc chloride, Phillips (in which a quaternary salt is used and the stilbazole obtained by pyrolysis of the stilbazole methiodide) and the acetic anhydride one, showed the first two to be superior to the third52. All three methods give the mn -stilbazoles, i97a (b t see above), and under the conditions of the acetic anhydride method cis- are converted into tram-stilbazoles (p. 348). An exception appears to be the formation of the cis-stilbazole from 2-picoline and salicaldehyde with acetic anhydridei ". ... 

Hilton determined the hydroxyl number of polyesters and polyethers in the region 2.6-3.2 n in 0.5 hr rs 3.0 hr elapsed time required by the acetic anhydride method. He used 1-2% sample in a solvent system 1 9 CHCl3 CCl4 in 1-cm cells and reported no trouble due to the 0.5% ethanol present in the CHCI3 that he used. It was necessary to thermostat the cell-holder to 0.1° C to get precise absorbance readings. 

In some cases, it can be beneficial to cap unreacted amino groups after the completion of a coupling reaction three classical methods using acetic anhydride are explained below. However, this capping step is in most cases not a necessity, and it has been shown that the classic acetic anhydride method is not suited for automated peptide syntheses due to the low stability of the acetic anhydride solution. Alternative protocols have been developed using Z(2Cl)-OSu in NMP DCM DIEA [23]. The three methods described below can also be used for a M-terminal acylation of the final pepridyl-resin. 

International Organization for Standardization, Nonionic surface active agents— polyethoxy-lated derivatives—determination of hydroxyl value—acetic anhydride method, ISO 4326 1980. Geneva, Switzerland. 

---