Oxidation of secondary alcohol

3 Oxidation of Secondary Alcohols Oxidation of Insoluble Secondary Alcohols 

Good yields of ketones were obtained in the oxidation on Pt-Bi catalysts (Bi/ Pts = 0.5) of secondary alcohols insoluble in water under the same conditions as for cinnamyl alcohol oxidation (see Section 9.2.3.2). Table 2 shows that selectivity in excess of 95 % was obtained at 97-99% conversion [43]. 

Dihydroxyacetone (DHA), the oxidation product of the secondary hydroxy group of glycerol, is an artificial tanning agent in cosmetics and a pharmaceutical intermediate. Glycerol oxidation in acidic medium on a platinum-bismuth catalyst (Bi/ Pt atomic ratio = 3) prepared by coprecipitation of Pt and Bi salts, yielded 20 % DHA at 30 % conversion [70]. The deposition of bismuth on platinum particles by oxido-reduction (Bi/Pt = 0.13) yielded 37 % DHA at 70% conversion 

Mesoxalic acid (or ketomalonic acid) is a good chelating agent and potentially a valuable synthon for organic synthesis. It has been prepared by oxidation of sodium tartronate on PtBi/C catalyst at 60 °C without pH control the maximum yield was 65% at 80% conversion [67]. Operating at 80 °C, 50% mesoxalic acid was obtained at total conversion of tartronic acid. The solution was free from other oxidation products, which were totally oxidized to CO2. 

Mesoxalic acid selectivity of 95 % at complete conversion has been claimed in the oxidation of tartronic acid in the presence of Bi-Pt/C catalysts [108]. 

In secondary alcohols, there is only one hydrogen atom on the carbon atom bearing the — OH group. Therefore, secondary alcohols can be oxidised by only one degree. The end product of the oxidation is a ketone. 

---

A white solid, m.p. 178 C. Primarily of interest as a brominaling agent which will replace activated hydrogen atoms in benzylic or allylic positions, and also those on a carbon atom a to a carbonyl group. Activating influences can produce nuclear substitution in a benzene ring and certain heterocyclic compounds also used in the oxidation of secondary alcohols to ketones. 

By the oxidation of secondary alcohols with potassium dichromate and dilute sulphuric acid, for example ... 

Selective oxidation of secondary alcohols to ketones is usually performed with CrOj/HjSO, I I in acetone (Jones reagent) or with CrOjPyj (Collin s reagent) in the presence of acid-sensitive groups (H.G. Bosche, 1975 C. Djerassi, 1956 W.S. Allen, 1954). As mentioned above, a,)S-unsaturated secondary alcohols are selectively oxidized by MnOj (D.G. Lee, 1969 D. Arndt, 1975) or by DDQ (D. Walker, 1967 H.H. Stechl, 1975). 

Alcohols are oxidized slowly with PdCh. Oxidation of secondary alcohols to ketones is carried out with a catalytic amount of PdCh under an oxygen atmo-sphere[73.74]. Also, selective oxidation of the allylic alcohol 571 without attacking saturated alcohols is possible with a stoichiometric amount of PdfOAc) in aqueous DMF (1% H OifSll],... 

Oxidation of secondary alcohols to ke tones (Section 15 10) Many oxidizing agents are available for converting sec ondary alcohols to ketones PDC or PCC may be used as well as other Cr(VI) based agents such as chromic acid or po tassium dichromate and sulfuric acid... 

Oppenauer reaction is oxidation of secondary alcohols to ketones using aluminium t-butoxide... 

Aldehydes and ketones are among the most important of ail compounds, both in biochemistry and in the chemical industry. AUdehydes are normally prepared in the laboratory by oxidation of primary alcohols or by partial reduction of esters. Ketones are similarly prepared by oxidation of secondary alcohols or by addition of diorganocopper reagents to acid chlorides. 

Dichromate oxidation of secondary alcohols produces ketones in good yield, with little additional oxidation. For example, CH,CH2CH(OH)CH3 can be oxidized to CH CH2COCH3. The difference between the ease of oxidation of aldehydes and that of ketones is used to distinguish them. Aldehydes can reduce silver ions to form a silver mirror—a coating of silver on test-tube walls—with Tollens reagent, a solution of Ag1" ions in aqueous ammonia (Fig. 19.3) ... 

Furthermore, the oxidation of secondary alcohols with an equimolar amount of BTMA Br3 in the presence of a buffer such as aq. Na2HP04 or aq. CH3COONa afforded the corresponding ketones in good yields (Fig. 23). 

The complex Pd-(-)-sparteine was also used as catalyst in an important reaction. Two groups have simultaneously and independently reported a closely related aerobic oxidative kinetic resolution of secondary alcohols. The oxidation of secondary alcohols is one of the most common and well-studied reactions in chemistry. Although excellent catalytic enantioselective methods exist for a variety of oxidation processes, such as epoxidation, dihydroxy-lation, and aziridination, there are relatively few catalytic enantioselective examples of alcohol oxidation. The two research teams were interested in the metal-catalyzed aerobic oxidation of alcohols to aldehydes and ketones and became involved in extending the scopes of these oxidations to asymmetric catalysis. 

As with chromic acid, tertiary alcohols are oxidised only very slowly with degradation. The rate expression for oxidation of secondary alcohols is ... 

The oxidations of formic acid by Co(III) and V(V) are straightforward, being first-order with respect to both oxidant and substrate and acid-inverse and slightly acid-catalysed respectively. The primary kinetic isotope effects are l.Sj (25°C)forCo(IU)and4.1 (61.5 C°)for V(V). The low value for Co(lII) is analogous to those for Co(IIl) oxidations of secondary alcohols, formaldehyde and m-nitrobenzaldehyde vide supra). A djo/ h20 for the Co(III) oxidation is about 1.0, which is curiously high for an acid-inverse reaction . The mechanisms clearly parallel those for oxidation of alcohols (p. 376) where Rj and R2 become doubly bonded oxygen. 

Figure 6 Enantioselective oxidation of secondary alcohols with secondary alcohol dehydrogenase (SADH), from a thermophihc bacterium (log E is used in...

Secondary alcohol oxidases catalyze the oxidation of secondary alcohols to ketones using molecular oxygen as oxidant. A secondary alcohol oxidase from polyvinyl alcohol-degrading bacterium Pseudomonas vesicularis var. povalolyticus PH exhibited activity toward several... 

Oxidation of primary alcohols leads to aldehydes and oxidation of secondary alcohols leads to ketones. This oxidation also involves the loss of two hydrogen atoms. However, unlike the oxidations discussed so far in this chapter that are mediated almost exclusively by cytochromes P450, the major enzyme involved in the oxidation of ethanol is ALD (discussed earlier in this chapter) (74). Although ALD is the major enzyme involved in the oxidation of ethanol and most other low molecular-mass alcohols, cytochromes P450, especially 2E1, can also oxidize ethanol and this enzyme is induced in alcoholics. Although comprehensive studies have not been published, it appears that cytochromes P450 are often the major enzymes involved in the oxidation of higher molecular mass alcohols. 

N-bromosuccinimide is a selective oxidising agent and oxidises OH groups without disturbing other oxidisable groups. Thus while it does not oxidise aliphatic primary alcohols in presence of water it is highly selective for the oxidation of secondary alcohols to ketones. 

Thioanisolc. A system utilizing thio-anisole as an organic mediator was developed for the oxidation of secondary alcohols to ketones (Fig. 5 2-octanol to 2-octanone 99%, menthol to menthone 92%, cyclododecanol to cyclododecanone 75%) [43]. The use of 2,2,2-trifluoroethanol as a solvent in the mediatory system improved the yields [44]. 

TEMPO 2,2,6,6-Tetramethylpiperidinyl-1-oxy (20 TEMPO) works as a mediator for the oxidation of primary alcohols to aldehydes. The oxidation of secondary alcohols is much slower than that of primary alcohols as exemplified by the oxidation of (19) to (21) (Scheme 7) [48]. Active species is the oxo-ammonium generated from TEMPO. 

Scheme 25 Oxidation of secondary alcohols with thioanisole as organic redox catalysts.

The oxidation of secondary alcohols (66) to (67) is possible by indirect electrooxidation utilizing thioanisole as an organic redox catalyst in a PhCN-2,6-lutidine-Et4NOTs-(C/Pt) system at 1.5 V vs. SCE (Scheme 25) [81] and is also performed in the presence of 2,2,2-trifluoroethanol [82]. It is suggested that the initially formed cation radical sulfide species derived from the direct discharge of the sulfide provides phenylmethyl-alkoxysulfonium ions, which are transformed to (67) and thioanisole. 

A-Hydroxyphthalimide (88) has also been shown to be an effective mediator for the oxidation of alcohols [120]. The oxidation process depicted in Scheme 32 is suitable for the oxidation of secondary alcohols (86). A-Hydroxyphthalimide also plays an important role as a mediator for deprotection of the 4-phenyl-l,3-dioxolane... 

---