Esterification with oxalyl chloride

Crotonic acid, esterification with sec-butyl alcohol, 41, 60 Crystal Violet, from condensation of oxalyl chloride with dimethyl-aniline, 41, 2-4... 

The carboxylic functionalities inserted onto the tubes can be used as platforms to obtain further transformations (Fig. 3.5). A commonly utilized route is the reaction of carboxylic groups with thionyl chloride or oxalyl chloride to prepare the corresponding acyl chlorides, which are useful intermediates for amidation or esterification reactions. Amides can also be prepared directly from the acids by means of standard solution chemistry conditions, using carbodiimide derivatives in the presence of the selected amine. 

There are several chemical reactions that can be used as an alternative to achieve covalent functionalization of CNTs. Two of them are amidation and/or esterification reactions. Both reactions take advantage of the carboxylic groups sitting on the side-walls and tips of CNTs. In particular, they are converted to acyl chloride groups (-C0-C1) via a reaction with thionyl (SO) or oxalyl chloride before adding an alcohol or an amine. This procedure is very versatile and allows the functionalization of CNTs with different entities such as biomolecules [154-156], polymers [157], and organic compounds [158,159] among others. 

Esterification. Dimethylchloroformiminiuin chloride, generated in situ from DMF and oxalyl chloride (5, 251), converts carboxylic acids into an activated derivative, which reacts with alcohols or phenols in the presence of pyridine to form esters in 70-90% yield. The method is also useful for preparation of active esters from N-protected amino acids, since no racemization is observed. 

Typical procedure. 4,4 -Bis[(3-carbomethoxy)propyl]benzophenone 1268 [952] By a standard esterification procedure, 4-phenylbutyric acid was converted to its methyl ester 1267 in 92% yield. To carbon disulfide (100 mL) was added 50 g of this ester, followed by oxalyl chloride (17.4 g). The solution was cooled to 0 °C and anhydrous aluminum chloride (74 g) was slowly added. The mixture was then stirred at 25 °C for 3.5 h. The solvent was subsequently decanted from the heavy brown syrup that separated, and the syrup was stirred with 2 kg of ice. This mixture was extracted with diethyl ether, and the ethereal layer was washed with water, dried, and concentrated to a thick orange liquid, which was distilled to give 38.8 g (73%) of faintly yellow liquid bp 280-285 °C/2 mmHg. 

Reaction schemes 257,258 and 259 gave some examples of some modes of formation of this important class of pyrethroids. The technical processes however, in order to obtain products as pure as possible, consists of the esterification of the acid chloride. Particularly sensible optically active acid chlorides may be obtained by chlorination with the system oxalyl chloride/DMF at lower temperatures [789]. In case of free cyanohydrine an acid scavenger is necessary [789 a], Alternatively, zinc chloride catalyzes the addition of an acid chloride to the aldehyde 280 to give the a-chlorobenzyl esters [790], which easily react with sodium cyanide [791] to give particularly clean products [792]. 

The synthesis of the sterically hindered 2-ketoesters succeeded in a simple fashion and in excellent yields by the esterification of ethyl oxalyl chloride with the lithium salt of 2,6-di-f rt-butyl-4-methoxyphenol followed by the chemose-lective nucleophilic addition of methyl or ethyl Grignard reagents to the unsym-metrical ethyl aryl oxalate. Reaction with (S)-l-amino-2-(methoxymethyl)pyrro-... 

Esterification.—iVAWW -Tetramethylchloroformamidinium chloride, which is readily prepared from iVAWW -tetramethylurea and oxalyl chloride, is an efficient reagent for the esterification of carboxylic acids with alcohols yields of between 66 and 97% are obtained, and the method has also been applied to macrolide synthesis. A modified one-pot procedure for the esterification of carboxylic acids, using phenyl dichlorophosphate-dimethylformamide complex, has appeared. A simple method of activation of carboxylic acids, using methanesulphonyl chloride and triethylamine followed by addition of the alcohol and 4-dimethylaminopyridine, leads to esters in 57— 96% yield for thirteen examples. 0-Methylcaprolactim reacts with carboxylic acids to give methyl esters in 73—91 % yield for seven examples and 2-iodoethyl esters are prepared from acyl chlorides, ethylene oxide, and sodium iodide. Transesterification, catalysed by titanium(iv) alkoxides, provides an effective method for synthesis of esters. Diethyl trichloromethylphosphonate reacts with carboxylic acids to give ethyl esters via transesterification, in 52 to 98 % yield. ... 

A final synthetic effort in the yohimbine alkaloid area concerns the studies reported by Loewenthal and his coworkers (Scheme 3.92) (143). The aim was to develop an efficient method to prepare the bicyclic enone 21, which serves as a key intermediate in the Woodward reserpine synthesis strategy (19). The route for preparation of 21 began with Friedel Crafts reaction of 2-methoxynaphthalene (523) with the oxalyl chloride equivalent 524, a process which afforded the acenaphthenoquinone 525. Oxidative-decarboxylation of 525 yielded the naphthalene-carboxylic acid 526 which was transformed by Birch reduction and esterification to the dihydro-derivative 527. Carboxyla-tion then provided geminal diester 528 which was epoxidized. Sequential lactonization and methylation afforded tricyclic lactone 529. Ester cleavage with subsequent decarboxylation gave lactone 530 which was demethylated to provide 531. While no further effort was given to the development of this... 

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