Precursors, chemical

Finally, there are also pollutants that do not cause direct health impacts hut that may have the potential to cause harm indirectly, through their actions on the overall ecology, or as they function as precursor chemicals that lead to the production of other harmful chemicals. The major indirect-action pollutants include volatile organic carbon (VOC) compounds that act as precursors to more harmful species chemicals called halocarbons and chemicals called greenhouse gases. 

VOCs react in the presence of sunlight to produce photochemical smog, a mixture of organic chemicals that can irritate the eyes and other mucous membranes. VOCs also constitute a major precursor chemical leading to ozone production. VOC levels across the United States fell, on average, by 20.4 percent between 1989 and 1998. 

Metallo-organic CVD (MOCVD) is a specialized area of CVD, which is a relatively newcomer, as its first reported use was in the 1960s for the deposition of indium phosphide and indium anti-monide. These early experiments demonstrated that deposition of critical semiconductor materials could be obtained at lower temperature than conventional thermal CVD and that epitaxial growth could be successfully achieved. The quality and complexity of the equipment and the diversity and purity of the precursor chemicals have steadily improved since then and MOCVD is now used on a large scale, particularly in semiconductor and opto-electronic applications.91P1... 

Chemical Warfare Agent Precursor Chemicals Uses and Equivalents... 

Table F 1. Chemical warfare agent precursor chemicals uses and equivalents...

Precursor chemical CAS registry number Civilian uses CW agent production Units of agent per unit of precursor1... 

Appendix F is a list of precursor chemicals used in the synthesis of typical chemical warfare agents. 

The first two antidepressants, iproniazid and imipramine, were developed in the same decade. They were shown to reverse the behavioural and neurochemical effects of reserpine in laboratory rodents, by inhibiting the inactivation of these monoamine transmitters (Leonard, 1985). Iproniazid inhibits MAO (monoamine oxidase), an enzyme located in the presynaptic neuronal terminal which breaks down NA, 5-HT and dopamine into physiologically inactive metabolites. Imipramine inhibits the reuptake of NA and 5-HT from the synaptic cleft by their transporters. Therefore, both of these drugs increase the availability of NA and 5-HT for binding to postsynaptic receptors and, therefore, result in enhanced synaptic transmission. Conversely, lithium, the oldest but still most frequently used mood stabiliser (see below), decreases synaptic NA (and possibly 5-HT) activity, by stimulating their reuptake and reducing the availability of precursor chemicals required in the biosynthesis of second messengers. 

Although the above classes of raw materials are the most widely used, depending on the precursor chemical approach and desire for a specific level... 

Precursor Theory PCDD/Fs are formed from chemically related compounds as precursors. Chemically related products of PCDD/Fs are chloro-phenols and chlorobenzenes. Both classes of compounds are present in the... 

Poro-xylene is an industrially important petrochemical. It is the precursor chemical for polyester and polyethylene terephthalate. It usually is found in mixtures containing all three isomers of xylene (ortho-, meta-, para-) as well as ethylbenzene. The isomers are very difficult to separate from each other by conventional distillation because the boiling points are very close. Certain zeoHtes or mol sieves can be used to preferentially adsorb one isomer from a mixture. Suitable desorbents exist which have boiling points much higher or lower than the xylene and displace the adsorbed species. The boihng point difference then allows easy recovery of the xylene isomer from the desorbent by distillation. Because of the basic electronic structure of the benzene ring, adsorptive separations can be used to separate the isomers of famihes of substituted aromatics as weU as substituted naphthalenes. 

States members of the European Union. Most States and territories submitting form D are also furnishing the data on the licit movement of precursor chemicals. 

All of the major manufacturing and exporting countries have continued to provide comprehensive information on exports of substances in Tables I and II of the 1988 Convention. For 2003, Brazil has resumed reporting on exports of scheduled substances, notably potassium permanganate. As noted in paragraph 21 above, Canada and China, major traders in precursor chemicals, are now reporting their exports to the Board. 

With regard to controls applied by Governments to precursor chemicals, the Board notes with satisfaction that a number of countries, including... 

The majority of those countries apply the requirement of import and export authorizations at least over some precursor chemicals, and about 60 countries and territories are controlling the imports and exports of all 23 substances in Tables I and II. Moreover, 49 countries and territories have informed the Board of controls applied to a total of 155 substances currently not in Tables I or II of the 1988 Convention. 

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