Isotopic labelling tritium-labelled benzene

The crude reaction product purified by preparative GLC was subjected to Fourier-transform tritium NMR spectrometry to evaluate the isotopic composition of the labeled benzene. 

Labelling by tritium or deuterium provides a tool for measuring whether a proton in an organic molecule is labile and also a method for measuring the speed of ionisation. With tritium this is a simple method for even the slowest process because of the accuracy of counting this particular isotope [40]. For example even the rate of ionisation of benzene may be followed in this way. 

Kinetic isotope effects in the exchange reaction can, however, be evaluated by the use of a tritium label. Thus the ratio of the rates for protiodedeuteration (H+d-CeHsD), D, and protiodetritiation (H+-I-C6H5T), ki, may be determined and these d/ t values may be related to ksjkj) values by known equations (72, 13). In 81 percent H2SO4, the value is 1.5 for a single position of benzene, and 1.5, 1.7, and 1.9 for the meta, oitho, and para positions of toluene respectively (74). 

Water is poorly soluble in hydrocarbons and determination of its solubility by ordinary chemical analysis requires a large amount of hydrocarbon samples. The solubility of water in benzene (Joris and Taylor 1948) and other hydrocarbons (Black et al. 1948) was determined with the use of tritium ( H, T) as tracer. These studies give an example where correction for the mass difference between an element of natural isotopic composition and its radioactive tracer is necessary. Water labeled with T was prepared by bombardment of heavy water (D2O) with... 

Phase transfer catalysis has been exploited with beneficial effect in isotope exchange reactions. Chemically sensitive compounds that would not survive under the conventional base catalysis conditions can be labeled successfully. For example 23 was tritiated in benzene solution using HHO/NaOH/n-Bu4NBr, with a recovery of 80%, and the base-sensitive steroids 2A and were tritiated without double bond isomerization (location of tritium not reported) (Figure 3.11) ... 

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