Sulphur-containing molecules

The loss of methyl radical from the molecular ion of n-heptylmethyl-sulphide has been observed at short times ( 10 ps) following FI [520]. 

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In a variation of these reactions, Grieco and Masaki used p-toluenesulfonyl groups to direct alkylation reactions in the formation of carbon chains and then cleaved the sulphones with lithium in ethylamine. This type of synthetic construction involving the use of sulphur-containing molecules has become a typical sequence in organic syntheses. In this case, the reactions formed part of successful syntheses of squalene and sesquifenchene and were carried out without any migration or loss of stereochemical integrity of the double bonds. Similar sequences have been reported by Trost (prenylation reactions) and Marshall (synthesis of a cembranoid precursor). 

CATALYTIC PROPERTIES OF TRANSITION METAL SULPHIDES FOR THE DEHYDROGENATION OF SULPHUR CONTAINING MOLECULES. 

Transition metal sulphides are able to catalyze a very large number of reactions. The most important utilization concerns catalytic hydrotreating, but many others can be foreseen due to the resistance of these catalysts towards sulphur. For example, recent studies have demonstrated the interest of such catalysts for the selective conversion of carbon monoxide into hydrocarbons [1] or alcohols [2]. Until now, only few papers and patents report on the utilization of sulphides for fine chemical applications [3-6]. Nevertheless, this type of solids fits well to catalyze the reactions dealing with sulphur containing molecules. 

The objective of the present work is to classify the catalytic performances of unsupported transition metal sulphides (TMS) for these different reactions dehydrogenation of a sulphur containing molecule without sulphur elimination, hydrodesulphurization and hydrogenation. 

Moreover, this study points out the ability of sulphides to catalyze either reactions involving the conversion of sulphur containing molecules without desulphurization (DHN of THT) or desulphurization of these molecules (HDS of thiophene) as well as classical hydrogenation reactions (HN of BP). These properties make the sulphide catalysts interesting to be applied to organic chemistry, particularly in thiochemistry. 

Investigation of the electronic properties of sulphur-containing molecules... 

Within the last two decades, significant progress has been achieved in the theoretical computation of NMR spectroscopic parameters,110 particularly of nuclear screening constants. Theoretical calculations of 33S NMR parameters have received a certain attention for two main reasons (i) they can help in identifying and elucidating the structural properties of sulphur-containing molecules, and (ii) they can provide important information on the electron distribution and bonding situation around the sulphur atom. 

In the previous section we have discussed several cases in which bimetallic bonding increases the overall reactivity of a system towards sulphur. If the opposite occurs, such a phenomenon could be useful for the prevention of sulphur poisoning. In practical terms, the idea is to find bimetallic systems that have a good catalytic activity and are less sensitive to the presence of sulphur-containing molecules in the feedstream than pure metals. Sn/Pt and Pd/Rh satisfy these requirements [26-29]. 

There are some different approaches to extend gas oil hydrotreating technology so as to increase sulphur compounds conversion to reach the new specification of 500 ppm. At this lower level the most difficult sulphur-containing molecules in gas oil have to be removed. 

The rate of removal sulphur-containing molecules increases as follows ... 

These undesirable components tend to be nitrogen-, oxygen- or, to a lesser extent, sulphur-containing molecules. In the past, selective adsorbents such as clay or bauxite were used to remove impurities but these processes were messy and gave waste disposal problems. 

Papers on the photo-oxidation of sulphur-containing molecules have been published. a-Lipoic acid has been oxidized by a variety of reagents, including 102.190 The complex mixture of products contains the four possible thiolsul-phinates and two possible thiolsulphonates. Stevens et a/.191 have calculated the rate constant for interaction of a-lipoic acid with 1Oa. The photo-oxidation of dimethyl sulphide in the gas phase,192 of dibutyl sulphide in ethanolic solution,193 and of the drugs thioridazine194 and chlorpromazine195 has been explored. 

Transient Species.—Pioneering studies by Johnson and co-workers have shown that monomeric thioformaldehyde is generated when methane reacts with small sulphur-containing molecules, such as carbon disulphide, carbonyl sulphide, or hydrogen sulphide, at low pressure in a radio-frequency discharge tube. On the basis of these results, Johns and Olson prepared thioformaldehyde, under slightly different conditions, from dimethyl disulphide in the presence of sulphur hexafluoride. The reaction path suggested was ... 

During vulcanisation, the brass surface is exposed to active sulphur-containing molecules present in the rubber compound and a strong bond is formed between the rubber compound and the tyre cord by the action of an interfacial, non-stoichiometric Cu S layer (x 1.8)... 

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