Oxidation with Sodium Dichromate

In a 2-L, three-necked flask fitted with a mechanical stirrer, a dropping funnel, and a reflux condenser, a solution of 120 g (0.400 mol, 20% excess) of sodium dichromate dihydrate and 135 g (1.33 mol) of 96% sulfuric acid in 500 mL of water is added over a 40-min period to a well-stirred mixture of 128.0 g (1.00 mol) of 4-ethylcyclohexanol in 200 mL of water. Within 2 min, the mixture becomes greenish-black, and the temperature rises from 30 to 68 °C during the addition of the first half of the oxidizing solution. Immediately after the addition has been completed, the temperature starts dropping and, within 5 min, decreases to 55 °C. The mixture is cooled and extracted twice with 400 mL of ether-pentane (3 1). The extracts are washed several times with water, dried, and evaporated to yield 113.6 g (90%) of 4-ethylcyclohexanone bp 109-112 °C at 50 mm of Hg. 

---

Removal of the ketal protecting groups, followed by oxidation with sodium dichromate ia acetic acid gave... 

The starting materials of the aldehyde method may be sulfonated. For example. Cl Acid Blue 9 [2650-18-2] Cl Food Blue 2 (Cl 42090), is manufactured by condensing a-(A/-ethylanilino)-y -toluenesulfonic acid with o-sulfobenzaldehyde. The leuco base is oxidized with sodium dichromate to the dye, which is usually isolated as the ammonium salt. In this case, the removal of the excess amine is not necessary. However, this color caimot be used in the food sector because separation of the chromium compounds from the dye is difficult. An alternative method which gives food-grade Cl Acid Blue 9 (14) and dispenses with the use of sodium dichromate employs oxidative electrolysis of the leuco base (49). 

Terephthalic acid has been obtained from a great many /)-disubstituted derivatives of benzene or cyclohexane by oxidation with permanganate, chromic acid, or nitric acid. The following routes appear to have preparative value from />-toluic acid, />-methylacetophenone,2 or dihydro-/)-tolualdehyde by oxidation with permanganate from f>-cymene by oxidation with sodium dichromate and sulfuric acid from />-dibromobenzene or from /i-chloro- or -bromobenzoic acid by heating at 250° with potassium and cuprous cyanides and from />-dibromo-benzene, butyllithium, and carbon dioxide. ... 

Compound 87 (R = r-Bu, R = Ph, R = H) has been prepared by addition of tert-butylmagnesium chloride to 1-phenylphthalide (102) and subsequent dehydration with p-toluenesulfonic acid. It is described as a yellow oil with brilliant fluorescence under UV light, which on oxidation with sodium dichromate yields diketone 103. Compound 87 (R = /-Bu, R = Ph, R = H) with dimethyl acetylenedicarboxylategives 104(mp 128-129 C, 80%) on reduction 105 is obtained 105 is also accessible from 87 (R = <-Bu, R = Ph, R = H) and dimethyl maleate (mp 151-152°C, endo) a maleic anhydride adduct has also been described (mp 147.5-148°C, 83%). Diels-Alder adducts have been also prepared from the benzo[c]furan precursors 106 (R = CHjPh, R = H, Ph) in the presence of catalytic amounts of acid 107 (mp 141-142.5X, 70%) and 108 (mp 140-141.5°C, 49%) were obtained, which on catalytic hydrogenation (Pd/C) gave the exo isomers 109(110-1 irC) and 110(90-92°C, 125.5-127°C, dimorphism). The basis for these stereochemical assignments remains unclear, however. Compounds... 

Benzoin can be oxidized to the a-diketone, benzii, very efficiently by nitric acid or by copper(II) sulfate in pyridine. On oxidation with sodium dichromate in acetic acid the yield is lower because some material is converted into benzaldehyde by cleavage of the bond between two oxidized carbon atoms and activated by both phenyl groups (a). Similarly, hydrobenzoin on oxidation with dichromate or permanganate yields chiefly benzaldehyde and only a trace of benzii (b). 

Chromic acid is also the reacting compound in oxidations with sodium dichromate or potassium dichromate in dilute sulfuric acid [641, 642, 643, 644, 1146], perchloric acid [621, 655], or acetic acid [627, 628], Modifications lie in the use of excess chromic acid [536] and of additional solvents such as benzene [627], ether [536, 641], or dimethyl sulfoxide [629] and in the control of the reaction temperature at 50-55 °C [644], 30-68 °C [642], 25 [536, 641], or 0 "C [536]. Results of some of the different procedures... 

The compound can be prepared by direct oxidation with sodium dichromate of 2-ethyl-6-methylpyr-azine (0.10) as described by Wolt (1975b). 

Oxidation with sodium dichromate. Primary and secondary alcohols are oxidized to aldehydes and ketones in 80-90% yield by Na2Cr2 07 2H2O and sulfuric acid in DMSO at 70° (90 min.). DMSO is not involved and acts as a solvent. In its absence, considerable charring occurs with further oxidation of the carbonyl product. Cr03 can also be used as oxidant. ... 

In this particular instance an altogether new compormd para-toluidine shall be formed which upon oxidation with sodium dichromate and sulphuric acid shall rmdergo aromatic ring oxidation instead, because anilines with strong oxidizing agents, e.g., dichromate usually gives similar products. 

The first account of 10,12-indeno[2,l-h]fluorene dione 17 dates to 1951 when Deuschel condensed phenylbenzoylacetylene (125) with ketodiester 126 to afford wt-terphenyl diester 127 (Scheme 37) [26], Saponification of 127 to 128 and subsequent ring closure yielded 11-hydroxy-[2, l-h]IF dione 129. Reduction using Zn metal provided 10,12-dihydro [2,l-h]IF 100. A final oxidation with sodium dichromate gave dione 17. 

---