Aqueous hydroxide

Phenol s chemical properties are characterized by the influences of the hydroxyl group and the aromatic ring upon each other. Although the stmcture of phenol is similar to cyclohexanol, phenol is a much stronger acid. Its piC in aqueous solution at 25°C is 9.89 x 10 ° (8). This characteristic allows aqueous hydroxides to convert phenol into their salts. The salts, especially those of sodium and potassium, are converted back into phenol by aqueous mineral acids or carboxyhc acids. 

In one process developed by Cams Corp., Illinois, poUucite is digested with sulfuric acid to cesium alum that is dissolved in an aqueous hydroxide solution to form cesium alum hydroxide and potassium sulfate, from which cesium permanganate is direcdy precipitated by addition of potassium permanganate (28). 

Dica.rboxyIic AcidMonoesters. Enzymatic synthesis of monoesters of dicarboxyUc acids by hydrolysis of the corresponding diesters is a widely used and thoroughly studied reaction. It is catalyzed by a number of esterases. Upases, and proteases and is usually carried out in an aqueous buffer, pH 6—8 at room temperature. Organic cosolvents may be added to increase solubiUty of the substrates. The pH is maintained at a constant level by the addition of aqueous hydroxide. After one equivalent of base is consumed the monoesters are isolated by conventional means. 

The common method of preparation of 6-alkyl-2,4-dioxotetrahydro-triazines is the cyclization of acyl-biurets by aqueous hydroxide. Formyl biuret which should by analogy 3deld 5-azauracil had not been known until recently. Its transient formation can be expected during further synthesis of 5-azauracil. Piskala and GuP achieved... 

In 2,4-disubstituted quinazolines, the 4-position reacts fastest with nucleophiles, generally even when the 4-substituent is a poorer leaving group. 2,4-Dichloroquinazoline undergoes mono-substitution at the 4-position with alcoholic alkoxides (25°, 2 hr, 80-98% yield), phenolic phenoxide (20°, 16 hr, 50% yield), aqueous hydroxide (30°, 3 hr), alcoholic methylmercaptide (20°, exothermically), alkylamines (20°, 10-60 min, 100%... 

Oxidation of methyl perfluoroalkyl sulphones with refluxing aqueous potassium permanganate produced the perfluorinated alkanesulphonic acid in 85% yield as the potassium salt (equation 86). On the other hand, attempted oxidation with sodium hypochlorite caused only chlorine substitution (equation 87). Reaction of the new sulphone with aqueous hydroxide gave the same perfluoroalkane sulphonic acid salt (equation 88). 

The exchange between the ruthenium anions RuO and RuO " in aqueous hydroxide media has been found rapid. A limit for the rate coefficient at 0 °C of > 1.7x10 l.mole . sec has been proposed by Luoma and Brubaker. The isotopic method ( ° Ru), and separation procedures based on the precipitation of the Ru04 or RuOJ species with barium or tetraphenylarsonium ions, respectively, were used. Attempts to use an esr technique failed. 

Before preparing these carbon-supported Pt-based catalysts, a support pretreatment toward granular activated carbon with an aqueous solution of NaOH (pH 14) was carried out by immersing for 24 h to promote the anion exchange between the ligand chloride of impregnated metal precursers (K2PtCl4) and the aqueous hydroxide ion (OH ) inside the micropores of the activated carbon [33]. 

Ashour, S.S., Rinker, E.B. 6c Sandall, O.C. (1996) Absorption of chlorine into aqueous bicarbonate solutions and aqueous hydroxide solutions. AIChE Journal, 42(3), 671—682. 

Bis [(trifluoromethyl)thio] acetaldehyde (83a) has been prepared from an enam-ine precursor (84), although refluxing in aqueous ethanolic HCl is required to effect this reaction.The aldehyde is less stable than its enol tautomer (83b), and many reactions typical of aldehydes fail. For example, addition of aqueous silver nitrate immediately yields the silver salt of (83b), rather than giving precipitation of (elemental) silver. The (trifluoromethyl)thio substituent has pseudohalogenic character and, together with the hydroxy group, stabilizes the alkene tautomer in the manner of a push-pull alkene. The enol-aldehyde equilibrium mixture in acetonitrile shows an apparent of 2.6 when titrated with aqueous hydroxide. 

Hydrolysis of FCIO3 is very slow even at 250°-300°C 92). For quantitative hydrolysis, heating of FClOg with concentrated aqueous hydroxide solution to 300°C in a sealed tube is required ... 

There is one report of competitive nucleophilic attack at the amide carbonyl in an Ai-acyloxy-A-aUtoxyamide. Shtamburg and coworkers have reported that MeONa reacted with Ai-acetoxy-A-ethoxybenzamide (159) in DME giving methyl and ethyl benzoate (160 and 161) (Scheme 26) . They attributed the formation of methyl benzoate to the direct attack of methoxide ion at the amide carbonyl rather than at nitrogen. The formation of 161 was attributed to a HERON reaction. Though not mentioned by the authors, it seems likely that under these aprotic conditions, 162 could also have been formed by methoxide attack at the acetate carbonyl leading to an anion-induced HERON reaction, by analogy with the reaction of Ai-acyloxy-Ai-alkoxyamides and aqueous hydroxide discussed above (Section IV.C.3.c)... 

Acidity of phenols Phenols are fairly acidic compounds. Aqueous hydroxides, e.g. NaOH, convert phenols into their salts (not by aqueous bicarbonates). 

Aldehyde formation Reimer-Tiemann reaction Treatment of a phenol with chloroform (CHCI3) and aqueous hydroxide introduces an aldehyde group (—CHO) onto the aromatic ring, generally ortho to the —OH group. A substituted henzalchloride is initially formed, but is hydrolysed by the alkaline medium. Salicylaldehyde can be produced from phenol by this reaction. Again, salicylaldehyde could be oxidized to sahcylic acid, which could be acetylated to aspirin. 

These results can be rationalized by picturing the crystal violet carbonium ion as solubilized and oriented in the micelle, followed by attack by the aqueous hydroxide ion. The catalytic effect of the micellar solution has a twofold origin a concentration effect and an... 

Variations in the differences, A, between pK FUO) and p 2 (mixed solvent) for each individual solvent composition are relatively small (Tables I, II), indicating that Reaction 4 for different substituted benzaldehydes is influenced almost equally by the change in solvent composition. This fact, together with the existing evidence (19) that for aqueous hydroxide solutions substituted benzaldehydes form a suitable set of J indicators, proves that substituted benzaldehydes can be used also for the establishment of J scales in water-ethanol and water-DMSO mixtures. 

Where there are two carbonyl groups to stabilize the amide anion, as in the l,2-benzenedicarboximide (phthalimide) anion (Section 18-IOC), the acidity increases markedly and imides can be converted to their conjugate bases with concentrated aqueous hydroxide ion. We have seen how imide salts can be used for the synthesis of primary amines (Gabriel synthesis, Section 23-9D and Table 23-6). 

The most important reactions of nitroalkan.es are those involving the a hydrogens of the primary and secondary compounds. For example, nitro-methane is sufficiently acidic to dissolve in aqueous hydroxide solutions. The anion so produced has an electronic structure analogous to the nitrate anion ... 

The kinetics and equilibrium of protium-deuterium exchange between pentafluoro-ethane and aqueous hydroxide ion have been studied.125... 

Fig. 5.10 Carbanion formation and alkylation via interfacial deprotonation using concentrated aqueous hydroxide solution.

Rate equations of this type are normally associated with the formation of associative intermediates or the involvement of deprotonated ligand forms in reactions with two (or more) competitive pathways. However, in the case of octahedral metal complexes of ligands such as 2,2 -bipyridine or 1,10-phenanthroline, such mechanisms do not appear to be likely. Associative mechanisms would involve seven-co-ordinate intermediates, which are likely to be sterically strained and electronically disfavoured on ligand field grounds. Furthermore, this type of ligand does not appear to contain any strongly acidic protons which are likely to be involved in reactions with aqueous hydroxide ion (but see later). 

Excess ethylamine can be allowed to react with the hydrogen chloride formed in the acylation reaction. Alternatively, equimolar amounts of acyl chloride and amine can be used in the presence of aqueous hydroxide as the base. 

The critical treatment of studies of hydroxide catalysis in H20-D20 mixtures is handicapped by the comparative uncertainty of the value of the fractionation factor 0L for the hydroxide ion (or, perhaps, doubts about the proper formulation of the aqueous hydroxide ion), as was discussed in Section VB3. 

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