Carboxylic acids with silver oxide

In solution-phase peptide synthesis, acylation of amino acids or peptides with N-protected azetidine-2-carboxylic acid is performed via the active esters, e.g. A-hydroxysuccin-imide 100 111-112 or pentachlorophenyl ester, m 117 as well as by the mixed anhydride 101114 or carbodiimide 118 methods. An attempt to prepare the A-carbonic acid anhydride by cycli-zation of A-(chloroformyl)azetidine-2-carboxylic acid with silver oxide in acetone or by addition of triethylamine in situ failed, presumably due to steric hindrance. 111 In SPPS, activation of the Fmoc-protected imino acid by HBTU 119,120 is reported. In solution-phase peptide synthesis, coupling of N-protected amino acids or peptides to C-protected azetidine-2-carboxylic acid or related peptides may be performed by active esters, 100 118 121 mixed anhydrides, 95 or similar methods. It may be worth mentioning that the probability of pip-erazine-2,5-dione formation from azetidine-2-carboxylic acid dipeptides is significantly reduced compared to proline dipeptides. 111 ... 

Mechanism The mechanism of the oxidation of aldehydes to carboxylic acid with silver oxide is given in Scheme 7.15. 

Benzenediazonium-2-carboxylate and its substituted derivatives have been prepared by diazotization of anthranilic acids in the presence of hydrochloric acid followed by dehydrochlorination of the resultant diazonium carboxylate hydrochlorides with silver oxide. 

The reagent of choice for the conversion of aldehydes into carboxylic acids is silver oxide, which is often prepared in situ from silver nitrate in alkaline medium [3(55]. Enanthol heated with silver oxide affords enanthoic acid [77]. 3-Cyclohexene-l-carboxaldehyde (1,2,3,6-tetrahydrobenzalde-hyde) gives a 62.5% yield of the carboxylic acid on treatment with silver nitrate and ethanolic potassium hydroxide at room temperature [3(55] (equation 347). 

In the Hunsdiecker reaction, the silver salt of a carboxylic acid, prepared by treating the acid with silver oxide, is treated with a halogen. Bromine is the usual reagent, but iodine may also be used. Carbon dioxide is evolved and the corresponding alkyl halide is obtained, usually in fair to good yield. 

Pyridazine aldehydes and ketones with the carbonyl group at the ring or in a side chain react in the usual manner. They form hydrazones, semicarbazides, oximes, etc. Side-chain aldehydes can be easily oxidized to pyridazinecarboxylic acids with silver nitrate and side-chain ketones are oxidized to carboxylic acids by treatment with potassium permanganate or hydrogen peroxide. 

Isothiazole-3-carboxylic acid and its 4-bromo derivative have been obtained by oxidation of the corresponding aldehydes with silver oxide. They form acid chlorides, esters, and amides. The amides may be dehydrated to give the corresponding nitriles. ... 

The "silver mirror test" is used to distinguish an aldehyde from a ketone. Tollen s reagent, Ag(NH3)20H, acts as an oxidizing agent. When it is mixed with an aldehyde, the aldehyde oxidizes to the salt of a carboxylic acid. The silver ions in Tollen s reagent are reduced to silver atoms, and coat the glass of the reaction container with solid silver metal. 

Effective conditions for oxidation of aldehydes to carboxylic acids with KMn04 involve use of t-butanol and an aqueous NaH2PC>4 buffer as the reaction medium.173 Buffered sodium chlorite is also a convenient oxidant.174 175 An older reagent for carrying out the aldehyde — carboxylic acid oxidation is silver oxide. 

Gol dfarb and Litvinov first formylated a thienothiophene. In Vilsmeier formylation of 2-ethylthieno[2,3- ]thiophene (20) the formyl group enters the vacant a-position, producing 5-ethyl-2-formylthieno-[2,3- ]thiophene 16%). Oxidation of the latter with silver oxide gives 5-ethylthieno[2,3-6]thiophene-2-carboxylic acid (55) identical with that formed by cydizing the ester of (5-ethyl-3-formyl-2-thienylthio)acetic... 

In the formation of SAMs, the film-forming molecules order themselves by chemical interaction with neighbouring molecules and with the substrate surface. This technique has been applied for a large variety of modifier/substrate combinations. Various sulphur compounds, like alkanethiols and (di)sulfides have been deposited on metals such as silver, copper and gold isocyanides on platinum and carboxylic acids on aluminum oxide and silver oxide.75 Alkyltrichlorosilanes have been deposited on gold, mica, aluminum, tin oxide and silicon oxide. The latter combination is of interest here. 

Oxidation of the aldehyde to a carboxylic acid was accomplished with silver oxide (see Section 10.14). 

Oxidizability is a chemical property characteristic of aldehyde functions. The aldehyde function of glucose makes it capable of reducing copper salts, and this property is widely used to assay sugars. Furthermore, many aldehydes oxidize to form carboxylic acid with oxidizing agents as weak as silver oxide ... 

An established procedure for the conversion of an aldehyde to a carboxylic add involves the use of Ag20 in the presence of NaOH [21, 22]. This has inspired researchers to employ different forms of Ag(I) compounds as catalysts in combination with an oxidant. Recently, a mild and selective method for the transformation of aldehydes into carboxylic acids with a silver catalyst was reported [23]. Thus, in the presence of 10 mol% AgN03 and 5 equiv. of 30% aq. H2O2 in acetonitrile at 50 °C, various aromatic, conjugated, and aliphatic aldehydes were readily oxidized to the corresponding carboxylic acids in good yields. 

Didehydroretinol (289), which is referred to as vitamin A2 in the earlier literature, was oxidized with manganese(IV) oxide to the aldehyde (290), which reacted further with silver oxide to give the carboxylic acid (291) (Barua and Nayar, 1968). 

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