Alcohols, secondary, oxidation hypochlorite

Secondary alcohols are oxidized at room temperature to ketones in high yields by HOCl generated in situ from aqueous NaOCl and acetic acid (109,110). Selective oxidation in the presence of a primary alcohol is possible. In methanol, aldehydes are oxidized to methyl esters (110). Under the proper conditions, alcohols can be esterified with HOCl forming isolable alkyl hypochlorites. 

Although NaI04 or KI04 are the secondary oxidants used in the vast majority of cases in which alcohols are oxidized with catalytic Ru04, the employment of sodium hypochlorite (NaOCl),31 sodium bromate (NaBrOj )32 or Cl+, electrolytic-ally generated by oxidation of chloride ion,33 have also been reported. 

Apart from sodium hypochlorite, a number of alternative secondary oxidants for TEMPO-mediated alcohol oxidations can be employed. These include cerium (IV) ammonium nitrate (CAN),24 trichloroisocyanuric acid (TCCA),25 oxone ,26 MCPBA,2,3,7 PhI(OAc)2,27 W-chlorosuccinimide,28 sodium bromite,29 electrooxidation,8,21 H5IO626 and a polymer-attached diacetoxybromide (I) complex.30... 

The very common TEMPO-mediated Anelli s protocol for the oxidation of alcohols, involving a biphasic CH2Cl2-water mixture containing catalytic TEMPO, or an analogue thereof, and sodium hypochlorite as a secondary oxidant, shows a great selectivity for the oxidation of primary alcohols in the presence of secondary ones9 and has found some use in Synthetic Organic Chemistry.10... 

Primary and secondary alcohols are easily oxidized by a variety of reagents, including chromium oxides, permanganate, nitric acid, and even household bleach (NaOCl, sodium Oxidation hypochlorite). The choice of reagent depends on the amount and value of the alcohol. We of AI CO h OIS use cheap oxidants for large-scale oxidations of simple, inexpensive alcohols. We use the most effective and selective reagents, regardless of cost, for delicate and valuable alcohols. 

The stable, commercially available nitroxyl radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) 51 is an excellent catalyst, in conjunction with a co-oxidant, for the oxidation of alcohols. The most popular co-oxidant is buffered sodium hypochlorite (NaOCl). Oxidation of the nitroxyl radical gives the oxoammonium ion 52, which acts as the oxidant for the alcohol to form the carbonyl product. Primary alcohols are oxidized faster than secondary and it is often possible to obtain high chemoselectivity for the former. For example, oxidation of the triol 53 gave the aldehyde 54, with no oxidation of the secondary alcohols (6.44). The use of TEMPO is particularly convenient for the oxidation of primary alcohols in carbohydrates, avoiding the need for protection of the secondary alcohols. 

In the experiments that follow, several representative oxidations of alcohols using hypochlorous acid will be performed. In the first experiment, cyclodode-canol (1), a secondary alcohol, is oxidized to cyclododecanone (2) using sodium hypochlorite or commercial household bleach (Eq. 16.20). In the second experiment, 4-chlorobenzyl alcohol (3) is oxidized directly to 4-chlorobenzoic acid (4) using calcium hypochlorite (Eq. 16.21). 

Hypochlorite ion is an effective oxidizing agent for a variety of substrates when the reactions are conducted under phase transfer conditions [13]. Tetrabutylammonium ion catalyzes the reaction of hypochlorite with benzylic alcohols in dichloromethane or ethyl acetate solution to yield alcohols and ketones. Likewise, secondary alcohols are oxidized to ketones according to equation 11.6. The results of a series of such... 

Oxidative Methods.—A convenient and inexpensive procedure for the oxidation of secondary alcohols to ketones, applicable to multi-mole preparations, uses aqueous sodium hypochlorite in acetic acid/ Selective oxidation of secondary alcohols is possible as primary alcohols are oxidized much more slowly. Alcohol oxidations with molecular bromine in combination with nickel(ll) benzoate in acetonitrile are remarkably free from competing reactions. However, 1,4-diols yield butyrolactones. ... 

In another procedure, oxidation is carried out in the presence of chloride ions and ruthenium dioxide [31]. Chlorine is generated at the anode and this oxidises ruthenium to the tetroxide level. The reaction medium is aqueous sodium chloride with an inert solvent for the alkanol. Ruthenium tetroxide dissolves in the organic layer and effects oxidation of the alkanol. An undivided cell is used so that the chlorine generated at the anode reacts with hydroxide generated at the cathode to form hypochlorite. Thus this electrochemical process is equivalent to the oxidation of alkanols by ruthenium dioxide and a stoichiometric amount of sodium hypochlorite. Secondary alcohols are oxidised to ketones in excellent yields. 1,4- and 1,5-Diols with at least one primary alcohol function, are oxidised to lactones while... 

Nickel(lll) oxide, prepared from a nickel(ii) salt and sodium hypochlorite, is used for the oxidation of alkanols in aqueous alkali [46]. Residual nickel(Ii) oxide can be re-activated by reaction with sodium hypochlorite. Nickel oxides have also long been used in the manufacture of the positive pole in the Edison nickel-iron rechargeable battery, now largely superseded by die lead-acid accumulator, and in the Jungner nickel-cadmium batteries used as button cells for calculators [47]. Here, prepared nickel oxide is pressed into a holding plate of perforated nickel. Such prepared plates of nickel(lli) oxide have been proposed as reagent for the oxidation, in alkaline solution, of secondary alcohols to ketones and primary alcohols to carboxylic acids [48]. Used plates can be regenerated by anodic oxidation. 

A convenient procedure for the oxidation of primary and secondary alcohols was reported by Anelli and co-workers (8,9). The oxidation was carried out in CH2CI2 with an aqueous buffer at pH 8.5-9.5 utilizing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1) as the catalyst and KBr as a co-catalyst. The terminal oxidant in this system was NaOCl. The major disadvantage of using sodium hypochlorite or any other hypohalite as a stoichiometric oxidant is that for each mole of alcohol oxidized during the reaction one mole of halogenated salt is formed. Furthermore,... 

Oxidation of CHOH (7, 337). Sodium hypochlorite solutions1 oxidize secondary alcohols dissolved in acetic acid to ketones in yields of 90-95%. Selective oxidation in the presence of a primary alcohol group is possible. The oxidation has been conducted, with suitable precautions, on a large scale.2... 

In 1980, Stevens et al.10 reported that a plain solution of sodium hypochlorite, which is easily available as swimming pool chlorine , is able to efficiently oxidize secondary alcohols in a solution in acetic acid, while primary alcohols react very slowly. Two years later, this research team published11 a more detailed account on the ability of NaOCl/AcOH to perform the selective oxidation of secondary alcohols in the presence of primary ones. Stevens oxidant became one of the standard reagents for the selective oxidation of secondary alcohols.12... 

General Procedure for Selective Oxidation of Secondary Alcohols in Presence of Primary Alcohol, Using Stevens Protocol (Sodium Hypochlorite in Acetic Acid)... 

Sodium hypochlorite (household bleach) and acetic acid offers a very cheap and effective alternative to Jones reagent for the oxidation of secondary alcohols to ketones and has been widely used for the synthesis of ketones. 

Is there a more environmentally friendly reagent available to accomplish the oxidation of alcohols Recently, it has been shown that sodium hypochlorite (NaOCI) in acidic solution is an excellent reagent for the oxidation of secondary alcohols to ketones. Examples are shown in the following equations ... 

Many reagents are available to oxidize a simple secondary alcohol to a ketone. Most labs would have chromium trioxide or sodium dichromate available, and the chromic acid oxidation would be simple. Bleach (sodium hypochlorite) might be a cheaper and less polluting alternative to the chromium reagents. DMP and the Swem oxidation would also work. 

As mentioned before a PEG-supported TEMPO proved to be very efficient in the oxidation of 1-octanol to octanal not only with sodium hypochlorite, but also in combination with different terminal oxidants such as bis(acetoxy)iodobenzene and trichloroisocyanuric acid. This reaction could be extended to acyclic and cyclic primary and secondary alcohols with excellent results. It is remarkable that the PEG-supported TEMPO maintained the good selectivity for primary vs secondary ben-zylic alcohol oxidation typical of non-supported TEMPO. 

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