Anhydride Reagent

The other analytical methods necessary to control the typical specification given in Table 5 are, for the most part, common quality-control procedures. When a chemical analysis for purity is desired, acetylation or phthalation procedures are commonly employed. In these cases, the alcohol reacts with a measured volume of either acetic or phthalic anhydride in pyridine solution. The loss in titratable acidity in the anhydride solution is a direct measure of the hydroxyl groups reacting in the sample. These procedures are generally free from interference by other functional groups, but both are affected adversely by the presence of excessive water, as this depletes the anhydride reagent strength to a level below that necessary to ensure complete reaction with the alcohol. Both procedures can be adapted to a semimicro- or even microscale deterrnination. 

Protein functional groups able to react with anhydrides include the oc-amines at the N-terminals, the s-amine of lysine side chains, cysteine sulfhydryl groups, the phenolate ion of tyrosine residues, and the imidazolyl ring of histidines. However, acylation of cysteine, tyrosine, and histidine side chains forms unstable complexes that are easily reversible to regenerate the original group. Only amine functionalities of proteins are stable to acylation with anhydride reagents (Fraenkel-Conrat, 1959 Smyth, 1967). 

A recent study of wood modified with a variety of anhydride reagents has questioned the validity of the use of the H-H model when interpreting the moisture sorption isotherms of modified wood (Papadopoulos and Hill, 2003). This has shown that although modification with anhydride reagents leads to a reduction in both monolayer and... 

Nitric acid-acetic anhydride reagent has been used to synthesize N,N -Amitro-N,N -ethylenebisacetamide (58) from A, A -ethylenebisacetamide (57) the former is a secondary high explosive and a precursor to the powerful explosive ethylenedinitramine (Section 5.10). It is interesting to note that (58) is not formed when (57) is treated with nitric acid alone or with strong mixed acid. 

A purification procedure for synthetic peptides was devised, 85 which uses the sulfo-benzoic anhydride reagent of Wieland et a 1.1X61 to terminate unreacted amino groups at each synthetic step and Sulfmoc chloride1 7 (1, Scheme 13) to derivatize the deprotected full-length peptide at the end of the synthesis. 

The unusual copper nitrate-acetic anhydride reagent reacted with acetyl-acetone itself to form bis-(3-nitro-2,4-pentanediono) copper(II) (V), the same compound prepared by Nyholm (18). A novel elaboration of this reaction was treatment of hydrated chromium (III) nitrate with acetylacetone in acetic anhydride to yield a mixture of mono- and dinitrochromiumacetylacetonate (XI and XII). 

Among the unsaturated ketonucleosides may be classified the disaccharide derivative 74, which is an analog of the biologically active compound 68c. The key intermediate for the synthesis of this unsaturated ketodisaccharide nucleoside was the partially protected, disaccharide nucleoside 73, which was prepared by two separate routes,56 Treatment of 73 with the Me2SO-acetic anhydride reagent for two days at room temperature afforded 7-[2,3-di-0-benzoyl-4-0-(3-0-benzoyl-2,6-di-deoxy - / - d - glycero - hex - 2 - enopyranosyl - 4 - ulose) - 6 - deoxy - / - d -glycopyranosyl]theophylline (74), isolated crystalline.56... 

Epoxide formation is nearly suppressed when massively subeti-tuted olefine, such as 2,2,4-trimethyl-3-hexene among others, ate subjected to the chromic oxide-acetic anhydride reagent,42 Cyclo-hexene yields primarily 2-cyclohexenone and cyclohexane- 1,2-dione777 although some cyclohexane oxide appears to bo formed also (Eq, 111). 

Nitro compounds, labelled with carbon-14, have been used during the polymerization of styrene (40). It has been shown that picric acid, which is rather an inefficient inhibitor, formally resembles p benzoquinone with this monomer. It becomes incorporated in the polymer but most of it is included in polystyrene of comparatively low molecular weight. Most of the combined picric add can subsequently be removed by treatment with trifluoro-acetic anhydride reagent, showing that the picric acid is not held in the polymer by carbon-carbon bonds. Further, it was shown, by isotope dilution analysis, that most of the picric add removed from the polymer by this treatment appeared as the add. 

Thus, anhydride reagents may be used both to block functional groups and to convert an existing functional group into a carboxylic acid. 

Unless otherwise directed, accurately weigh the appropriate amount of the sample indicated in the table below, transfer it into a 250-mL glass-stoppered Erlenmeyer flask, and add 5.0 mL of pyridine-acetic anhydride reagent (mix 3 volumes of freshly distilled pyridine with 1 volume of freshly distilled acetic anhydride). 

Recently, some modified reaction conditions have been proposed to improve yields, particularly for aromatic carboxylic acids. A phosphonium anhydride reagent (11) made from triphenylphosphine oxide and triflic anhydride appears to induce reaction at low temperatures in common solvents giving high yields of 2-arylbenzi midazoles in 30-60 min at room temperature (Scheme 3.1.12) [78]. 

Once all of the solutions have been prepared, use the following procedure. Pipette 5 ml of the acetic anhydride reagent solution into each of two oven-dried Erlenmeyer flasks, followed by pipetting 5 ml of the 2-butanol solution into only one of the flasks and mark it flask B. Stopper both flasks and mix thoroughly for at least 15 min. Carefully pipette 45 ml of H2O over 2 5 min and allow the flask to cool to ambient temperature (5 10 min). Add 5 drops of the indicator solution and titrate with the NaOH solution to the violet... 

Diphenylboric Anhydride Reagent Diphenylboric Anhydride Reagent 283 Mobile phase Carbon tetrachloride. 

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