Phosphorus pentoxide activator

Methylene chloride was distilled from phosphorus pentoxide and stored over activated molecular sieves (4A). 

Triethylamine was fractionally distilled from lithium aluminum hydride under nitrogen and acryloyl chloride was distilled under nitrogen. 1,1,2-Trichlorotrifluoroethane (Freon 113) was distilled from phosphorus pentoxide under nitrogen. Azobisisobutyronitrile (AIBN) was used as received. Methyl ethyl ketone peroxide (MEKP) (9% Organic Peroxide VN 2550) was obtained from Witco. Alumina (neutral, Brockman activity 1, 80-200 mesh) was obtained from Fisher Scientific Co. All reagents were obtained from Aldrich unless otherwise specified. 

Orthophosphoric acid and pyrophosphoric acid are preferred catalysts. Phosphorus pentoxide is catalytically active but no conclusive evidence has been described to show whether or not its activity depends on the presence of traces of water as promoter. Copper pyrophosphate and acid phosphates of cadmium are also good catalysts that the former probably owes its activity to partial conversion to acid or acidic salt under the polymerization conditions seems to be shown by the fact that there is an induction period. A composite prepared by calcining kiesel-guhr impregnated with orthophosphoric acid (the so-called solid phosphoric acid ) has found wide commercial use. 

Bromo-2-naphthoic add (1, 98%, Sigma Chemical Co.), 3.5-dimethylphenol (2, >98%, Merck-Schuchard), 1,3-dicyclohexylcarbodiimide (DCC, 99%, Merck-Schuchard), and 4-(dimethylamino)pyridine (DMAP, 99%, Aldrich Chemical Co., Inc.) were used as received. Dichloromethane was distilled from phosphorus pentoxide and stored over activated molecular sieves (4A). 

Isoquinoline synthesis Bischler-Napieralski synthesis is used to synthesize isoquinolines. (3-phenylethylamine is acylated, and then cyclodehy-drated using phosphoryl chloride, phosphorus pentoxide or other Lewis acids to yield dihydroisoquinoline, which can be aromatized by dehydrogenation with palladium, for example in the synthesis of papaverine, a pharmacologically active isoquinoline alkaloid. 

By a suitable choice of activating reagents, primary and secondary alcohols can be selectively oxidized to carbonyl compounds in good yields at room temperatures. Typical activating reagents ate acetic anhydride, sulfur trioxide—pyridine, dicyclohexyl catbodiimide, and phosphorus pentoxide (40). 

An ethereal solution of 1 kg of cholesterol is added to 100 kg of a 10% aqueous-alcoholic horse extract. The resulting emulsion is stirred at 90°C for 1 hour, while the ether is distilled off. The water insoluble saponin-cholesterol precipitate is centrifuged and washed with cold water until the wash water is colorless. The precipitate is air-dried at room temperature. The resulting dust-fine powder is extracted with ether in a Soxhlet apparatus for 10 days. The residue is treated with 20 kg of methanol and the undissolved material is filtered off. The yellowish methanol solution is treated with activated charcoal until it is colorless. The methanol is distilled off in a vacuum, and the residue is dried over phosphorus pentoxide in a vacuum not exceeding 1 mm Hg. The yield of pure sodium escinate obtained thereby is about 0.8 kg (8%). 

Carboxylic acids can also be activated by converting them to their anhydrides. For this purpose they are dehydrated with concentrated sulfuric acid, phosphorus pentoxide, or 0.5 equivalents of SOCl2 (1 equivalent of SOCl2 reacts with carboxylic acids to form acid chlorides rather than anhydrides). However, carboxylic anhydrides cannot transfer more than 50% of the original carboxylic acid to a nucleophile. The other 50% is released—depending on the pH value—either as the carboxylic acid or as a carboxylate ion and is therefore lost. Consequently, in laboratory chemistry, the conversion of carboxylic acids into anhydrides is not as relevant as carboxylic acid activation. Nonetheless, acetic anhydride is an important acetylat-ing agent because it is commercially available and inexpensive. 

If the water is displaced from the perborate by the action of hydrogen peroxide it is possible to increase the content of active oxygen in the product up to about 30 % but suoh products are not sufficiently stable. A more stable product containing up to 20% of active oxygen can be prepared by dehydration of the oompound NaB02. H202.3 H20 over sulphurio aoid, or phosphorus pentoxide, or by drying under reduced pressure at a maximum temperature of 50 °C. 

Acetonitrile, obtained from J. T. Baker Chemical Co., was refluxed overnight with phosphorus pentoxide and then distilled under nitrogen onto freshly activated Linde 4A molecular sieves. The acetonitrile was stored over the molecular sieves for 24 hr before use. 

One of the mildest methods for preparing methylene acetals involves reaction of a diol with dimethoxymethane in the presence of a suitable activating agent such as phosphorus pentoxide,176 trimethylsilyl Inflate.177 or lithium bromide and p-toluenesulfonic acid.178 The reaction is also used to make methoxymethyl ethers (see section 4.4,1) from alcohols. Scheme 3,95 illustrates the simultaneous formation of a methoxymethyl ether and a methylene acetal from Shikimic Acid.169 The reaction was adapted to the synthesis of the methylene acetal moiety of the marine antitumour agent Mycalamide B [Scheme 3.96],179... 

The DP results rendered by most of these methods are low and inaccurate, especially when the celluloses are alkali-sensitive, i.e., contain carbonyl groups bringing about chain cleavage in alkaline solutions or active carbonyls, which initiate the stepwise depolymerization of the cellulose chains (known as the peeling reaction) according to the carbonyl elimination mechanism of Isbell et al. [416-420]. The most accurate method for DP determination in all celluloses is the nitration method, in which the cellulose is nitrated in a solution of nitric and phosphoric acids and phosphorus pentoxide, and dissolved in butyl acetate [420-422]. 

One of the advantages of using the acetic anhydride system is that the reaction can be perfoimed at room temperature, which is in contrast to a report that trifluoroacetic anhydride is an unsatisfactory activator at this temperature.Attempts have been made to use acylating activators such as benzoic anhydride, phosphorus pentoxide or polyphosphoric acid, although these tend to give lower yields of carbonyl compounds. ... 

Styrenes are available by dehydration of either a-arylethyl or /S-aryl-ethyl alcohols. The procedures were reviewed in 1S>49. /S-Phenylethyl alcohol loses water at 140° over a roixture of molten sodium and potassium hydroxides to give styrene, C,H5CH=CH2, in 57% yield. The 2,4-dimethyI derivative has been prepared in a similar manner from the primary alcohol. " Many substituted styrenes have been made by dehydration of methylarylcarbinols with potassium hydrogen sulfate, phosphorus pentoxide, or activated alumina. 1,1-Diphenyl-ethylene and 2-phenyl-2-butene are easily obtained by boiling the corresponding tertiary alcohols with dilute sulfuric acid. 

The second general method into the thiochrom-4-one ring involves the interaction of a thiophenol with compounds possessing a carbon atom bonded by at least two electron withdrawing groups, usually in the presence of a dehydrating agent (phosphorus pentoxide or poly-phosphoric acid). The first application of this was by Simonis and Elias and is illustrated in Eq. (19). The most successful active methylene substrates have been /3-ketoesters, i )3-cyanoketones, ... 

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