Anti-knock agents

PbEu (anti-knock agents), radiation and sound shields, in paints, high quality glass. World production 1980 4 0 megatonnes. Lead compounds are toxic and hazardous to health. 

Currently available CRMs A number of organolead (tetra- and triaUcyllead) compounds are commercially available to be used as calibrants. There are also a number of interesting CRMs an urban dust certified for trimethyUead and more appear to be in development The interest in organolead compotmds is, however, on the decline due to the gradual disappearance of the tetraethyl anti-knock agent from petrol. 

Lead is also used in organ pipes, of course. Other uses include the lead-acid battery, radiation shielding, ceramic glazes, and in lead glass. It is a toxic element, and its organic derivatives are also toxic. Tetraethyllead was used for many years as an anti-knock agent in petrol. 

The use of PbEt4 as an anti-knock agent in petrol depends in part on the ability of the ethyl radicals, generated on its thermal decomposition, to combine with radicals produced in the over-rapid combustion of petroleum hydrocarbons chain reactions which are building up to explosion (knocking) are thus terminated short of this. The complete details of how PbEt4 operates are not known, but there is some evidence that minute Pb02 particles derived from it can also act as chain-stoppers . 

Mono( 17-cyclopentadienyl) carbonyl complexes of Ti, Zr, and Hf have been noted only in the patent literature. A U.S patent issued to Ethyl Corporation in 1962 described the use of such complexes as anti-knock agents and lubricant additives. Two examples of complexes purported to have been made are shown below (115). 

Tetraethyl lead (anti-knock agent in gasoline)... 

Tetra ethyl lead (TEL) was used as an anti-knock agent in automotive gasoline. Small amounts were normally added. During the compression stroke TEL reacts with the air to form very small lead oxide particles. Give an explanation why you believe TEL would be an effective anti-knock agent. 

Organic heavy metal compounds are produced by the chemical industry (e.g. tetraethyl lead was produced and added to petrol as an anti knocking agent for more than 30 years in the UK, until unleaded petrol became available in the mid-1980s). They can also be synthesised in some living organisms (e.g. bacteria). 

It is known that a small amount of lead tetraethyl is effective as an anti-knock agent in gasoline engines. This effect is due to the inhibition of the gas-phase reaction by the lead or lead oxide derived from the lead tetraethyl.l o.si] The inhibitory action of lead compounds on hydrocarbon combustion is largely exerted in the gaseous phase of the combustion zone. 

Tetra-ethyl lead is added to petrol as an anti-knock agent. When the petrol is burnt in the engine, the organic lead is converted to inorganic compounds. Ethylene dibromide is added to the tetra-ethyl... 

Elements Ge, Sn, and Pb form many interesting varieties of organometallic compounds, some of which are important commercial products. For example, EuPb is an anti-knock agent, and organotin compounds are employed as polyvinylchloride (PVC) stabilizers against degradation by light and heat. Some examples and advances are discussed in the present section. 

Alkyl Pb compounds, mainly tetramethyl and tetraethyl Pb, are added to gasoline as anti-knock agents. The amount added varies from country to country but is generally in the range 200—1500/igml-1 Pb and this may be present as one or both of the Pb alkyl species mentioned. Unfortunately, it has been found that the Pb response in atomic absorption spectroscopy is dependent on the particular alkyl with which it is associated. Thus, unless it is known that only one particular Pb alkyl is present in a gasoline sample, it is not possible to employ a simple dilution procedure. Since the exact nature of the Pb species is seldom known for sure, then a general analytical method must ensure that the response from the various Pb alkyls is equalised in some manner. This is achieved by stabilisation with iodine and a quaternary ammonium salt. 

The use of cyclopentadienyl-carbon monoxide compounds of Mn, as anti-knock agents in fuels, has been known for some time. In recent years the use of methylcyclopentadienyl manganese tricarbonyl (MMT) as an antiknock agent for gasoline has become more widespread, due to the decline in use of Pb alkyl compounds. 

Jan 2000 The chemical is severely restricted. All uses as an anti-knock agent in vehicles are... 

As was mentioned earlier, however, it is not performance at any price, those days are gone. Tetraethyl lead was added to fuel as an anti-knock agent, with the lead emitted to atmosphere. With the awareness and regulatory controls that are now being put into place in Europe with REACH we can say with some confidence that were tetraethyl lead to be proposed as an anti-knock additive today, that it would not be allowed by the regulators. 

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