Carboxylic and aldehydes

Figure 30.3 C NMR spectrum of oxidized starch. (Signals at 171.6 and 180.5 ppm are attributed to carboxyl and aldehyde groups, respectively).

Recently, Hiller and Pacsu have shown that accurate results may be obtained in the absence of sodium chloride by a direct alkali titration of the carboxyl groups in purified cotton. The carboxyl group content found was 0.02%, but after oxidation with potassium permanganate solution, 0.126% was found. From these data it may be seen that both carboxyl and aldehydic groups are present in the original cellulosic... 

Cellulosic substances have been used in various fields from commodities to industrial materials after mechanical and chemical modifications. Especially because chemically modified cellulosics have some unique functional properties, and also because of their biodegradability in most instances, the chemistry of cellulose has become one of the major areas in cellulose science. Figure 12 illustrates the chemical structure of cellulose in terms of chemical modifications. "" Three hydroxyl groups in the glucose residue, one primary and the other two secondary, are the sites for substitution reactions, which are the most common in cellulose derivatizations. The (1 4)-/3-glycoside bonds and other functional groups such as carboxyls and aldehydes present in most cellulosic material as minor groups are also possible sites for chemical modifications. 

Barteauwas able to demonstrate for well-defined Ti02 and ZnO surfaces the activity and selectivity for C2 oxygenate (carboxylates and aldehydes) and hydrocarbon (alkynes) coupling reactions over these model metal oxide surfaces under UHV conditions that is typically only seen in organometallic systems in solution. 

The important aspect of their study relates to the stereochemical mode of addition in the most preferred transition state in (a) and (b). In model-(a). Re-face addition of enamine carboxylic acid on the Re-face of the aldehyde is the lowest energy addition leading to an enantiomeric excess of about 99% in favor of (2S,3S) stereoisomer and anti-diastereomer as the major product In model-(b), on the other hand, anti-face addition involving the Si-Re mode respectively between enamine carboxylate and aldehyde is of the lowest energy. This approach predicts... 

This is an example of the Doebner synthesis of quinoline-4-carboxylic acids (cinchoninic acids) the reaction consists in the condensation of an aromatic amine with pyruvic acid and an aldehj de. The mechanism is probably similar to that given for the Doebner-Miller sj nthesis of quinaldiiie (Section V,2), involving the intermediate formation of a dihydroquinoline derivative, which is subsequently dehydrogenated by the Schiff s base derived from the aromatic amine and aldehyde. 

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

Because of its volatility, the cobalt catalyst codistills with the product aldehyde necessitating a separate catalyst separation step known as decobalting. This is typically done by contacting the product stream with an aqueous carboxyhc acid, eg, acetic acid, subsequently separating the aqueous cobalt carboxylate, and returning the cobalt to the process as active catalyst precursor (2). Alternatively, the aldehyde product stream may be decobalted by contacting it with aqueous caustic soda which converts the catalyst into the water-soluble Co(CO). This stream is decanted from the product, acidified, and recycled as active HCo(CO)4. 

Chemistry of rosin. All three types of rosin consist primarily of C20 mono-carboxylic diterpene resin acids, the most common of which have the molecular formula C20H20O2. In addition, rosins contain small amounts of neutral and other acidic components (e.g. fatty acids in tall oil rosin). The neutral components of rosins are diterpene alcohols, hydrocarbons and aldehydes, and their contents generally vary between 5 and 15 wt%. 

Cyclocondensation of D-homocystine methyl ester hydrochloride (106) and aldehyde 105 in the presence of Ph3P yielded 9-(benzyloxycarbonyla-mino)-6-oxoperhydropyrido[2,l-f ][l,3]thiazine-4-carboxylate (107) and its diastereomer (97MIP4, 98USP5710129). 

I Oxidation of a primary alcohol or an aldehyde yields a carboxylic acid (Sections 17.7 and 19.3). Primary alcohols are often oxidized with C1O3 in aqueous acid, and aldehydes are oxidized with either acidic Cr03 or basic silver oxide (Tollens reagent). 

The adjacent iodine and lactone groupings in 16 constitute the structural prerequisite, or retron, for the iodolactonization transform.15 It was anticipated that the action of iodine on unsaturated carboxylic acid 17 would induce iodolactonization16 to give iodo-lactone 16. The cis C20-C21 double bond in 17 provides a convenient opportunity for molecular simplification. In the synthetic direction, a Wittig reaction17 between the nonstabilized phosphorous ylide derived from 19 and aldehyde 18 could result in the formation of cis alkene 17. Enantiomerically pure (/ )-citronellic acid (20) and (+)-/ -hydroxyisobutyric acid (11) are readily available sources of chirality that could be converted in a straightforward manner into optically active building blocks 18 and 19, respectively. 

Carboxylic acids can be prepared by oxidizing primary alcohols and aldehydes with a strong oxidizing agent, such as acidified aqueous potassium permanganate solution. In some cases, an alkyl group can be oxidized directly to a carboxyl group. This process is very important industrially. 

Anhydrides, both aliphatic and aromatic, as well as mixed anhydrides of carboxylic and carbonic acids, have been reduced to aldehydes in moderate yields with disodium tetracarbonylferrate Na2Fe(CO)4. Heating a carboxylic acid, presumably to form the anhydride, and then reaction with Na/EtOH leads to the aldehyde. 

This reaction illustrates the striking difference in behavior between carboxylic esters on the one hand and aldehydes and ketones on the other. When a carbanion such as an enolate ion is added to the carbonyl group of an aldehyde or ketone (16-41), the H or R is not lost, since these groups are much poorer leaving groups than OR. Instead the intermediate similar to 146 adds a proton at the oxygen to give a hydroxy compound. 

Aldol-Type Reactions between Carboxylic Esters or Amides and Aldehydes or Ketones... 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and alkenes. The most common is the reaction with carboxylic acids, illustrated above.Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesi-toic acid. This method has the advantage over 18-13 and 18-14 that it is just one laboratory step from the acid to the amine, but conditions are more drastic. Under the acid conditions employed, the isocyanate is virtually never isolated. 

Condensation between carboxylic esters and aldehydes or ketones Addition of a-metalated esters to ketones Oxidation of methylene to OH, O2CR, or OR... 

Reaction between aldehydes, ammonia, and aldehydes, ketones, or carboxylic esters (Mannich)... 

Fig. 11. The metal sites in D. gigas hydrogenase (Hase) (A) and aldehyde oxidore-ductase (AOR) (B). The figure emphasizes the relative positioning of the metal sites Emd their proximity, suggesting an attractive electron transfer pathway. The arrows indicate electron trsmsfer for hydrogen evolution requiring an electron donor (A) Emd aldehyde conversion to carboxylic acid, the electrons being transferred to Em electron acceptor (B).

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

On the other hand, following the same sequences from the differently protected serine-derived nitrone 168, through the formation of hydroxylamines 169, C2 epimers of carboxylic acid and aldehydes are obtained, i.e., (2S,3R)-170 and (2S,3R)-171. Moreover, the syn adducts 164 were exclusively obtained in the addition of Grignard reagents to the nitrone 163, whereas the same reactions on nitrone 168 occurred with a partial loss of diastereoselectivity [80]. Q, j6-Diamino acids (2R,3S)- and (2R,3R)-167 can also be prepared from the a-amino hydroxylamines 164 and 169 by reduction, deprotection and oxidation steps. The diastereoselective addition of acetylide anion to N,N-dibenzyl L-serine phenyhmine has been also described [81]. 

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