Alcohols, general oxidation

Primary and secondary alcohols are readily oxidi2ed to aldehydes and ketones under alkaline conditions. Aldehydes, both aUphatic and aromatic, are converted into the corresponding carboxyUc acids. Ketones are generally oxidation resistant unless sufficient alkaU is present to effect enolization. The enol can be oxidatively cleaved. 

Manufacturing procedures for producing dye dispersions are generally not disclosed. The principal dispersants in use include long-chain alkyl sulfates, alkaryl sulfonates, fatty amine—ethylene oxide condensates, fatty alcohol—ethylene oxide condensates, naphthalene—formaldehyde—sulfuric acid condensates, and the lignin sulfonic acids. 

Chromic acid oxidations of 2° alcohols generally give ketones in excellent yields if the temperature is controlled. 

Generally, primary aliphatic alcohols are oxidized to their respective aldehydes, secondary aliphatic and aromatic alcohols to the corresponding ketones, and allyl and benzyl alcohols to their carboxylic acid or carboxylate ions. For instance, 2-propanol, acetaldehyde, and methyl-benzoate ions are oxidized quantitatively to acetone, acetate, and terephtalate ion respectively, while toluene is converted into benzoate ion with an 86% yield. Controlling the number of coulombs passed through the solution allows oxidation in good yield of benzyl alcohol to its aldehyde. For diols,502 some excellent selectivity has been reached by changing the experimental conditions such as pH, number of coulombs, and temperature. 

Adogen has been shown to be an excellent phase-transfer catalyst for the per-carbonate oxidation of alcohols to the corresponding carbonyl compounds [1]. Generally, unsaturated alcohols are oxidized more readily than the saturated alcohols. The reaction is more effective when a catalytic amount of potassium dichromate is also added to the reaction mixture [ 1 ] comparable results have been obtained by the addition of catalytic amounts of pyridinium dichromate [2], The course of the corresponding oxidation of a-substituted benzylic alcohols is controlled by the nature of the a-substituent and the organic solvent. In addition to the expected ketones, cleavage of the a-substituent can occur with the formation of benzaldehyde, benzoic acid and benzoate esters. The cleavage products predominate when acetonitrile is used as the solvent [3]. 

Tungsten-catalysed oxidation of alcohols by hydrogen peroxide is achieved in high yield in the presence of tetra-n-butylammonium hydrogen sulphate [20-22]. Secondary alcohols are converted into ketones (>90%) [e.g. 21], but primary alcohols generally are oxidized completely to the carboxylic acids [21], Aldehydes are also oxidized to the carboxylic acids [e.g. 21]. In contrast, using procedure 10.7.8.B, which is adaptable to scale up, benzyl alcohols are converted into the aldehydes benzoic acids are only formed with an excess of hydrogen peroxide [22],... 

B. General Oxidation Procedure for Alcohols. A sufficient quantity of a 5% solution of dipyridine chromium (VI) oxide (Note 1) in anhydrous dichloromethane (Note 7) is prepared to provide a sixfold molar ratio of complex to alcohol. This excess is usually required for complete oxidation to the aldehyde. The freshly prepared, pure complex dissolves completely in dichloromethane at 25° at 5% concentration to give a deep red solution, but solutions usually contain small amounts of brown, insoluble material when prepared from crude complex (Note 8). The alcohol, either pure or as a solution in anhydrous methylene chloride, is added to the red solution in one portion with stirring at room temperature or lower. The oxidation of unhindered primary (and secondary) alcohols proceeds to completion within 5 minutes to 15 minutes at 25° with deposition of brownish-black, polymeric, reduced chromium-pyridine products (Note 9). When deposition of reduced chromium compounds is complete (monitoring the reaction by gas chromatography or thin-layer chromatography analysis is helpful), the supernatant liquid is decanted from the (usually tarry) precipitate and the precipitate is rinsed thoroughly with dichloromethane (Note 10). 

The nickel oxide electrode is generally useful for the oxidation of alkanols in a basic electrolyte (Tables 8.3 and 8.4). Reactions are generally carrried out in an undivided cell at constant current and with a stainless steel cathode. Water-soluble primary alcohols give the carboxylic acid in good yields. Water insoluble alcohols are oxidised to the carboxylic acid as an emulsion. Short chain primary alcohols are effectively oxidised at room temperature whereas around 70 is required for the oxidation of long chain or branched chain primary alcohols. The oxidation of secondary alcohols to ketones is carried out in 50 % tert-butanol as solvent [59], y-Lactones, such as 10, can be oxidised to the ketoacid in aqueous sodium hydroxide [59]. 

These are relatively rare reactions for RuO - as with primary alcohols, further oxidation to carboxylic acids normally occurs. Examples are given in Table 3.3. Generally, under neutral conditions, aldehydes are formed but under acidic or alkaline conditions carboxylic acids are the main oxidation products. 

CHO - COOH. This hydroperoxide oxidizes aldehydes to carboxyjic acids in generally satisfactory yields. The oxidation is conducted in CH2Cl2Na2C03 or C lljOll-NaOH. The oxidant does not attack alcohols. The oxidation, as in epoxidations with 1, can be effected with H202 and a catalytic amount of 1. 

Mass spectrometer analyses of the fractions taken at regular intervals indicate the optimum conversions of aromatic hydrocarbons directly to aldehydes and alcohols by oxidation, as shown in Table III. Semiquanti-tative yields derived from low voltage mass spectral intensities and values found by gas chromatography were generally in good agreement—for example, oxidations of toluene and p-xylene, worked up after 2 hours, gave the results shown in Table IV. 

The above criteria apply in the case of isolated hydroxyl groups but when additional polar substituents are placed in the vicinity of the substrate hydroxyl the oxidation rate can be expected to change. Allylic hydroxyls are generally oxidized more rapidly than their saturated counterparts. Burstein and Rin-gold have studied the chromic acid oxidation of steroidal allylic alcohols in some detail and have found that the quasi-equatorial 3)3-isomer is oxidized more... 

---