Dichromate, hydrolysis

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

Arsenic trioxide may be made by burning arsenic in air or by the hydrolysis of an arsenic trihaUde. Commercially, it is obtained by roasting arsenopyrite [1303-18-0] FeAsS. It dissolves in water to a slight extent (1.7 g/100 g water at 25°C) to form a weaMy acidic solution which probably contains the species H AsO, orthoarsenous acid [36465-76-6]. The oxide is amphoteric and hence soluble in acids and bases. It is frequendy used as a primary analytical standard in oxidimetry because it is readily attainable in a high state of purity and is quantitatively oxidized by many reagents commonly used in volumetric analysis, eg, dichromate, nitric acid, hypochlorite, and inon(III). 

Trimethylacetic acid may be made by the hydrolysis of tert-butyl cyanide with weak hydrochloric acid at ioo0.1 It is also obtained by oxidation of trimethylpyroracemic acid with silver oxide or potassium dichromate and sulfuric acid,2 by oxidation of tertf-butylethylene with permanganate solution,3 or by oxidation of dimethyl 2,2-propanol with chromic acid.4 Schroeter reports the formation of trimethylacetic acid by rearrangement of the oxime of trimethylacetophenone to give the anilide of trimethylacetic acid, which can be hydrolyzed to give the acid.5... 

The aldehyde function at C-85 in 25 is unmasked by oxidative hydrolysis of the thioacetal group (I2, NaHCOs) (98 % yield), and the resulting aldehyde 26 is coupled to Z-iodoolefin 10 by a NiCh/CrCH-mediated process to afford a ca. 3 2 mixture of diaste-reoisomeric allylic alcohols 27, epimeric at C-85 (90 % yield). The low stereoselectivity of this coupling reaction is, of course, inconsequential, since the next operation involves oxidation [pyridinium dichromate (PDC)] to the corresponding enone and. olefination with methylene triphenylphosphorane to furnish the desired diene system (70-75% overall yield from dithioacetal 9). Deprotection of the C-77 primary hydroxyl group by mild acid hydrolysis (PPTS, MeOH-ClHhCh), followed by Swem oxidation, then leads to the C77-C115 aldehyde 28 in excellent overall yield. 

Ring D inversion seems to be a crucial step in biogenetic transformations of protoberberines to related alkaloids such as rhoeadine, retroprotoberberine, spirobenzylisoquinoline, and indenobenzazepine alkaloids. 8,14-Cyclober-bin-13-ol 478 derived from berberine (15) was successively treated with ethyl chloroformate, silver nitrate, and pyridinium dichromate (PDC) in dimethyl-formamide to give the keto oxazolidinone 479 (Scheme 98). Heating of 479 with 10% aqueous sodium hydroxide in ethanol effected hydrolysis, retro-aldol reaction, cyclization, and dehydration to provide successfully the... 

Addition of the dehydrated salt to acetic anhydride caused an exothermic reaction which accelerated to explosion. Presence of acetic acid (including that produced by hydrolysis of the anhydride by the hydrate water) has a delaying effect on the onset of violent reaction, which occurs where the proportion of anhydride to acid (after hydrolysis) exceeds 0.37 1, with an initial temperature above 35°C. Mixtures of dichromate (30 g) with anhydride-acid mixtures (70 g, to give ratios of 2 1, 1 1, 0.37 1) originally at 40°C accelerated out of control after 18, 43 and 120 min, to 160, 155 and 115°C, respectively. 

Dimethylaminobenzaldehyde has been made by the condensation of chloral with dimethylaniline, and subsequent hydrolysis 1 by the hydrolysis of tetramethyldiaminobenzhydrol with acetic acid 2 by the condensation of dimethylaniline, formaldehyde and m-sulfo-/>-tolyI hydroxylamine followed by hydrolysis 3 by the electrolytic reduction of a mixture of sodium nitrobenzene sulfonate, dimethylaniline and formaldehyde, and subsequent hydrolysis 4 by the reduction of a mixture of dimethylaniline, formaldehyde and sodium nitrobenzene sulfonate with iron and hydrochloric acid, followed by hydrolysis 5 by the condensation of alloxan with dimethylaniline followed by hydrolysis 6 by the condensation of dimethylaniline, formaldehyde and sodium -toluidine sulfonate in the presence of hydrochloric acid and potassium dichromate followed by hydrolysis.7 The most satisfactory method, however, is the condensation of dimethylaniline, formaldehyde and nitroso dimethylaniline, followed by hydrolysis,8 a method which was first described by E. Noelting and later perfected in detail by L. Baumann. 

Probably the most detailed study of the acid(HA)- and base(B)-catalyzed reactions of complex ions concerns the hydrolysis of the dichromate ion ... 

It has also been suggested to reduce the nitro group to an amino group, protect it with an acetyl protection, oxidize the sulfur atom to a sulfone using potassium dichromate, and then remove the protective acetyl group by hydrolysis [48-50]. 

In the presence of such reagents as bromate, iodate or dichromate, the rate of oxidation is independent of the nature or concentration of the oxidising agent, but is the same as the rate of decomposition to sulphate and sulphite, so that it is evident that hydrolysis is the first stage in the oxidation.2... 

Quinuclidine aldehydes are important synthetic intermediates. All three monoformylquinuclidines are known 2- and 3-formylquinucli-dines (75 and 76) were prepared 139,140 by reduction of JV-methyl-quinuclidinecarboxanilides with calculated amounts of LiAlH4 or by reduction of ethyl quinuclidinecarboxylates with NaAlH4. 4-Formyl-quinuclidine (77) was made by oxidation of quinuclidyl-4-carbinol (78) with potassium dichromate.87 3-Formylquinuclidine (76) was also synthesized from quinuclidin-3-one (2) by reaction with methoxy-methylene triphenylphosphorane and hydrolysis of the 3-methoxy-methylenequinuclidine (79) with hydrochloric acid.141... 

A DIE of k 2o/k )2o = 3.2 has been found in the hydrolysis of a-benzoyloxystyrenes, 382, in concentrated perchloric acid solution450. The rate of hydrolysis was found to be linear with the acidity function, Ho- A small inverse deuterium KIE, A h /I d = 0.78, at the -carbon has been found in the oxidation of cinnamic and crotonic acids451 by quinolinium dichromate. The reaction involves electrophilic attack on the double bond and a carbonium-ion intermediate (p = —4.0). A small inverse D KIE (k /k ->) = 0.80, p = —4.0] has been also observed452 in the acid cleavage of substituted styrenes by quinolinium dichromate in DMF in the presence of acid452. 

An improved route to the key intermediate 326 was also developed (165). Namely, 322 was converted to the monoprotected 1,4-dione 327 by sequential addition of the Grignard reagent derived from 2-(2-bromoethyl)-2-methyl-l,3-dioxolane followed by oxidation of the resulting benzylic alcohol with pyridin-ium dichromate (PDC). The ketone 327 was then smoothly transformed to the 2-azadiene 328 by olefination with BAMP. The regioselective addition of n-butyllithium to 328 as before followed by alkylation of the resulting metalloenamine with benzyl A-(2-bromoethyl)-A-methylcarbamate and acid-catalyzed hydrolysis furnished 325, which was converted to the cyclohexenone 326 by base-induced cycloaldolization and dehydration. 

Rai and Serne, 1977 Amacher and Baker, 1982). Both elements can exist in multiple oxidation states in aqueous environments. Chromium can exist in trivalent and hexavelent states, while Pu can occur in trivalent, quadrivalent, pentavalent, and hexavalent states. Additionally, both elements can exist as cationic or anionic species in aqueous systems. Trivalent Cr exists as the cation Cr3+ and its hydrolysis products, or as the anion CrO at very low concentrations. Hexavalent Cr occurs as the dichromate Cr207 or chromate HCrO or CrO anions, depending on pH. Plutonium exists in cationic states such as Pu3+ and Pu02 and anionic forms such as Pu02(C030H ). 

Note the color of the dry crystals of ammonium chromate and ammonium dichromate. Do either have the odor of ammonia Dissolve 1 gram of the chromate in as little water as possible. Note whether the solution has an odor of ammonia. What is its color (yellow like K2CrC>4 or orange like K2Cr207) Write equation for the hydrolysis of (NH CrCh and explain why it should hydrolyze more than K2CrC>4. 

In addition to chromate and dichromate, trichromatc, (CrjOutr . exists. Postulate a structure for the trichromate ion. Compare its structure to that of (PiOk, . Trichromale hydrolyzes in water. Predict the hydrolysis products. 

Methods of Chemical Analysis. During oxidation and hydrolysis studies of ferrous sulfate solutions, ferrous iron concentrations which ranged from 570 to 157 ppm were analyzed by titration with potassium dichromate solution using sodium diphenylamine sulfonate as an indicator (22). The same method was used to analyze for ferrous iron in mixed ferric-ferrous sulfate solutions. Total dissolved iron concentrations, which ranged from 560 to 100 ppm during hydrolysis of mixed ferric-ferrous... 

Two reactions illustrate the use of air oxidation where toxic selenium dioxide or bromination followed by hydrolysis and oxidation would normally be used. The first (4.39) oxidizes a methylphenol to a phenolaldehyde in 95% yield.195 The second (4.40) uses air to oxidize a pinene to verbenone in 77% yield.196 This eliminates the need for the lead tetraacetate, sodium dichromate, sulfuric... 

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