Action prolonging, methods

Titanium tetrafluoride may be prepared by the action of elemental fluorine on titanium metal at 250°C (5) or on Ti02 at 350°C. The most economical and convenient method is the action of Hquid anhydrous HF on commercially available titanium tetrachloride in Teflon or Kynar containers. Polyethylene reacts with TiCl and turns dark upon prolonged exposure. The excess of HF used is boiled off to remove residual chloride present in the intermediates. 

The procedure for preparing 6-hydroxynicotinic acid is also based on a method described by von Pechmann. 6-Hydroxynico-tinic acid has also been prepared by decarboxylation of 6-hy-droxy-2,3-pyridinedicarboxylic acid by heating 6-hydra-zinonicotinic acid or its hydrazide with hydrochloric acid by the action of carbon dioxide on the sodium salt of a-pyridone at 180-200 and 20 atmospheres by heating the nitrile of 6-chlo-ronicotinic acid with alcoholic sodium hydroxide or hydrochloric acid from 6-aminonicotinic acid and by the prolonged action of concentrated ammonium hydroxide on methyl cou-malate. ... 

Difluorobiphenyl has been prepared from 4,4 -biphenyl-bis-diazonium piperidide (by diazotizing benzidine and coupling with piperidine) and concentrated hydrofluoric acid 1 by the action of sodium on -fluorobromobenzene in ether 2 from benzidine by tetrazotization and decomposing the biphenyl-bis-diazonium salt with concentrated hydrofluoric acid 3 by the above method in the presence of ferric chloride 4 and by the prolonged contact of the vapors of fluorobenzene with a red-hot wire.5 The method described here is the most satisfactory for... 

As has been mentioned, preparation of esters of the C-17 hydroxyl group of selected progestins affords compounds with prolonged action. Similar chemical treatment of a corticoid would almost certainly lead to an ester of the sterically more accessible primary alcohol at C-21. In an interesting method for achieving esterification of the more hindered and less reactive tertiary 17-hydroxyl, prednisolone... 

A. Penicillin G structure and origin mode of action of penicillins methods for prolonging duration of action... 

Methods for Reducing Toxic Effects. The usefulness of methods and treatments for reducing peak absorption and reducing the body burden of carbon tetrachloride are rather limited due to the chemical s rapid rates of absorption and tissue disposition. On the other hand, investigations of antidotal therapy based on the mechanism of action has been limited to a few studies involving the administration of compounds to reduce free radical injury. Additional studies would be useful to better establish the effectiveness of both acute and prolonged antidotal therapy, since carbon tetrachloride is persistent in the body. 

Besides the foregoing method of refining, two others, long followed to some ex toot, are known—the first is a modification of Besbemer s process, and the second Is one patented by Mr. Parry of the Ebbe Yolo Iron Works. In (he first, the action of the blast is stopped when the melted iron has passed to the state of refined metal but as the iron prepared in this way has never been used in the manufacture of tin plates, it will he needless to prolong the description. The metal purified from common Welsh pig contains centcslmally—... 

A convenient method of preparing arsenic pentasulphide is to boil arsenic pentoxide with piperazine, when a solution is obtained which, by the prolonged action of hydrogen sulphide, yields the compound As2S5.3C4H10N2.3H2S if this is treated with cold dilute hydrochloric or acetic acid, crystals of arsenic pentasulphide are formed.6... 

The above illustrates the action of nitric acid in oxidising only one or two, and not all of the alkyl groups present, unless the heating is very prolonged. In the next preparation Method I. shows how chromic acid or alkali bichromate and sulphuric acid completely oxidises all the side chains present Method II. indicates how to oxidise completely the partially oxidised compound, potassium permanganate being sufficient. 

Isatoic anhydride has been prepared by prolonged refluxing of a mixture of anthranilic acid and ethyl chlorocarbonate,2 a reaction usually accompanied by formation of considerable monoethyl or/and diethyl isatoate or by action of phosgene upon anthranilic acid in a solution the acidity of which is moderated by occasional addition of sodium carbonate.2 The method described is based upon a patented procedure 3 in which, under conditions not fully specified, phosgene is passed into a solution of anthranilic acid hydrochloride with no subsequent adjustment of the acidity. 

---