Catalytic process

Details Catalytic process Catalytic process

1996-07-22

1999-01-12

Shippen, Michael L.

Chemistry: fischer-tropsch processes; or purification or recover

Group ib metal containing catalyst utilized for the...

423249, 423376, 4234182, 518700, 518722, 558 35, 562847, 568840, 568473, 568474, 570258, C07C 2700

Patent

active

058590706

DESCRIPTION:

BRIEF SUMMARY
This invention relates to catalytic processes and to catalysts therefor.
There is an increasing interest in the production of chemical compounds from very small quantities of a reactant material, especially those containing radio-active isotopes of certain elements.
Thus various techniques can be employed to produce small quantities of primary reagents containing an element isotope having a relatively short half-life. Provided such primary reagents can be converted into a suitable compounds within a relatively short time so that the compound exhibits the desired radioactivity, such compounds can be used as tracers in medical applications, particularly diagnostic medical applications.
An example of a diagnostic technique employing short-lived radio-isotopes in tracer compounds is positron emission tomography (PET). In this technique a target is bombarded with protons, e.g. in a cyclotron, giving rise to radioisotopes. The isotope reacts to produce a radio-labelled primary reagent. For example .sup.11 C is produced by proton bombardment of a nitrogen target: the .sup.11 C then reacts with traces of oxygen present to give .sup.11 CO.sub.2 as a primary reagent. Since the half-life of .sup.11 C is of the order of 20 minutes, it is necessary that the conversion of the .sup.11 CO.sub.2 to the desired tracer is accomplished rapidly. The amount of .sup.11 CO.sub.2 produced is very small, typically less than 1 nanomole per liter (at STP) of the target.
Another .sup.11 C primary reagent that can be produced is .sup.11 CH.sub.4 (using a mixture of hydrogen and nitrogen as the target). Other radio-labelled isotopes that can be obtained by analogous methods include .sup.13 N, .sup.15 O, and .sup.18 F, and these likewise can be used to introduce the appropriate radio-label into a tracer compound. Thus other primary reagents such as .sup.13 NO.sub.2.sup.-, .sup.13 NO.sub.3.sup.- and .sup.13 NH.sub.4.sup.+ can be produced by proton bombardment of water as a target; primary reagents such as .sup.15 O.sub.2 can be made by deuteron bombardment of nitrogen, C.sup.15 O.sub.2 can be made by deuteron bombardment of nitrogen containing a small amount, e.g. 2-2.5% v/v, of carbon dioxide; and .sup.18 F.sub.2 from a neon target and .sup.18 F.sup.- from a .sup.18 O-enriched water target.
Heretofore the primary reagents have been converted into the desired compounds by conventional small scale chemical reaction techniques, often involving a number of separate reaction stages: for example with the primary reagent .sup.11 CO.sub.2, the .sup.11 CO.sub.2, possibly after a preliminary step of adsorbing the carbon dioxide on a molecular sieve from which it is subsequently desorbed by heating, may be reacted with lithium aluminium hydride to form .sup.11 CH.sub.3 OH which is then reacted with aqueous hydrogen iodide, or with diphosphorus tetraiodide, to give .sup.11 CH.sub.3 I which is then used as an alkylating agent to give a tracer compound having .sup.11 C-containing methyl groups. The conversion of the primary reagents to reactive intermediate reagents is often troublesome and gives inconsistent yields. Furthermore although attempts have been made to automate such techniques, a skilled radio chemist is often required.
Even with those primary reagents, e.g. .sup.15 O.sub.2, which can be used directly as tracer materials, purification is often necessary before such use, and presents problems.
It would be desirable to employ simple, automated, catalytic techniques to effect the conversion of many of the desired primary reagents into more reactive intermediate reagents, or to effect reactions of undesired contaminants so as to render purification more facile. However we have found that, largely because of the small amounts of the reagents, conventional catalytic methods present problems. In many cases there is an unacceptable delay between contacting the reagent with the catalyst and appearance of the desired product (by which term we include intermediates which are subsequently converted into other compounds) in the effluent from the cataly

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