Wilzbach procedure

WILZBACH PROCEDURE. Exposure of organic compounds to tritium gas yields tntiated products of high activity without extensive radiation damage. Concentrations of tritium ranging from 1 to 90 millicuries per gram have been obtained with quite varied compounds. 

Alternative methods for accelerating the Wilzbach procedure include irradiation with ultraviolet light,47-49 X-irradiation,45,50 use of microwaves,51 and addition of iodine.52 The accelerated labeling is... 

The Wilzbach procedure is a simple method of labelling organic compounds with tritium The substance is exposed to tritium gas in a sealed glass vessel for several days or weeks. During this period, some of the hydrogen atoms of the molecule to be labelled are substituted by H atoms. Chemical side reactions may take place however at the same time, e.g., unsaturated compounds may be partly or completely hydrogenated. Several firms carry out this type of labelhng on request [312]. 

The difficulties of the Wilzbach procedure arise in the working up of the tritiated substances and the purification of the compounds which suffer radiolysis during prolonged storage. TLC can be used successfully for this purification purpose also (see Fig. 93). 

Several authors have reported the analysis and purification by TLC, of substances which had been tritiated according to the Wilzbach procedure. Thus glycerol ethers [262], the insect hormone ecdysone [338], vitamin Dg [501] and other steroids [501, 513, 617] (see Fig. 93, p. 170) and cardiac glycosides [551] have been purified on silica gel G layers. Unsaturated fatty acids have been isolated by TLC on silver nitrate-impregnated silica gel layers [425, 628]. 

Exchange reactions may be carried out using tritiated solvent or tritiated gas, as in the Wilzbach method [19]. In the former procedure the sample is heated in a sealed tube with a hydrogen transfer catalyst and a tritiated solvent. In the Wilzbach procedure to which recourse is made only when... 

Kraus and Greer1 originally prepared a few organotin hydrides with considerable difficulty from the reaction between an organotin sodium compound and ammonium bromide or ammonium chloride in liquid ammonia. Their procedure remained the only synthetic route to these compounds for some 25 years until 1947 when Finholt, Bond, Wilzbach, and Schlesinger2 obtained the methyltin hydrides in a more facile manner by reducing a mixture of the methyltin chlorides with lithium aluminum hydride (lithium tetrahydroaluminate). 

Three types of radiation-induced procedures have been used including (a) recoil tritiation, (b) Wilzbach gas irradiation7 with its modifications, and (c) radiation synthesis.8 All these methods utilize high-energy ionizing radiation to achieve tritium incorporation. Wilzbach exchange7 is the most satisfactory of the three and has been the most widely used. Radiation synthesis is a relatively recent development of limited but valuable specificity. 

Although most Wilzbach labeling work published has concerned non-heterocyclic molecules, sufficient heterocyclic compounds have been tritiated by this procedure for satisfactory predictions of labeling patterns... 

Nystrom and co-workers (1959) applied the Wilzbach technique to H labeling of methyl esters of saturated fatty acids, and the anticipated substitution of hydrogen by tritium occurred. In this procedure, gram amounts of methyl esters of palmitic and stearic acids were exposed to 1 Ci of H2 at room temperature. The fatty acid esters were deposited as thin layers by solvent evaporation on the inside wall of 1- X 10-inch reaction tubes. Methyl laurate and methyl myristate, being liquid at room temperature, required sealed ampules equipped with break seals the ampules were rotated to provide a continuously renewed thin film during their exposure to 5 Ci of tritium gas. Purification of the tritiated methyl esters includes saponification and extraction of the free acid with diethyl ether. 

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