POLYMERISATION INHIBITOR

Catechol is produced by coproduction with hydroquinone starting from phenol. Other techniques such as coal extraction remain marginal. The installed capacities (- 25,000 t/yr) are now sufficient to cover the demand. Catechol is mainly used for synthesis in food, pharmaceutical, or agrochemical ingredients. A specific appHcation of / fZ-butylcatechol is as a polymerisation inhibitor. 

Aq methacrylic acid (90%) was satd with NaCl (to remove the bulk of the water), then the organic phase was dried with CaCl2 and distd under vacuum. Polymerisation inhibitors include 0.25% p-methoxyphenol, 0.1% hydroquinone, or 0.05% A/,A/ -diphenyl-p-phenylenediamine. 

In dry air and in the presence of polymerisation inhibitors methyl and ethyl 2-cyanoacrylates have a storage life of many months. Whilst they may be polymerised by free-radical methods, anionic polymerisation is of greater significance. A very weak base, such as water, can bring about rapid polymerisation and in practice a trace of moisture on a substrate is enough to allow polymerisation to occur within a few seconds of closing the joint and excluding the air. (As with many acrylic monomers air can inhibit or severely retard polymerisation). 

In one process the crude styrene is first passed through a pot containing elemental sulphur, enough of which dissolves to become a polymerisation inhibitor. The benzene and toluene are then removed by distillation. The elthylbenzene is then separated from the styrene and tar by passing this through two distillation columns, each with top temperatures of about 50°C and bottom temperatures of 90°C under a vacuum of about 35 mmHg. The tar and sulphur are... 

Hydrogen cyanide is highly endothermic. It polymerises violently when there is no inhibitor present. If the heat liberation brings the medium to 284°C, it causes the compound to detonate. The presence of a base catalyses the hydrogen cyanide polymerisation. Nevertheless, this reaction is inhibited by mineral acids. The most common polymerisation inhibitor is phosphoric acid. 

TLC-Raman laser microscopy (X = 514 nm) in conjunction with other techniques (IR microscopy, XRF and HPLC-DAD-ESI-MS) has been used in the analysis of a yellow impurity in styrene attributed to reaction of the polymerisation inhibitor r-butylcatechol (TBC) and ammonia (from a washing step) [795]. Although TLC-FT-Raman did not allow full structural characterisation, several structural elements were identified. Exact mass measurement indicated a C20H25O3N compound which was further structurally characterised by 1H and 13C NMR. 

The extreme hazards involved in handling this highly reactive material are stressed. Freshly distilled material rapidly polymerises at ambient temperature to produce a gel and then a hard resin. These products can neither be distilled nor manipulated without explosions ranging from rapid decomposition to violent detonation. The hydrocarbon should be stored in the mixture with catalyst used to prepare it, and distilled out as required [1], The dangerously explosive gel is a peroxidic species not formed in absence of air, when some l,2-di(3-buten-l-ynyl)cyclobutane is produced by polymerisation [2], The dienyne reacts readily with atmospheric oxygen, forming an explosively unstable polymeric peroxide. Equipment used with it should be rinsed with a dilute solution of a polymerisation inhibitor to prevent formation of unstable residual films. Adequate shielding of operations is essential [3],... 

Pseudomonas chloraphis cells were used first, and more recently Rhodococcus rhodochrus Jl. Cells are immobilised in polyacrylamide particles and used in column reactors operated at below 10°C. The acrylamide is produced in 100% yield, and is so pure that polymerisation inhibitors have to be added to prevent spontaneous polymerisation. Both acrylonitrile and acrylamide inhibit the nitrile hydratase the nitrile hydratase is extremely stable. Therefore acrylonitrile is fed to maintain a level of 6% resulting in the accumulation of acrylamide of 66% (w/v), after which is it simply decolourised and concentrated (Yamada and Kobayashi, 1996). 

This reaction is carried out using the steel pressure vessel and techniques described in Section 2.17.2, p. 97. To the dry pressure vessel add 7.46 g (0.05 mol) of co-nitrostyrene (Expt 6.136), about 0.1 g of hydroquinone (a polymerisation inhibitor) and 15 ml of dry toluene. Fit a rubber bung carrying a calcium chloride guard-tube and cool the vessel to — 78 °C in an acetone-Cardice bath. During the cooling process set up the acetone-Cardice... 

Fig. 4 Tubulin polymerisation inhibitors possessing an indole moiety as a core structure...

Details A yellow coloured crystalline sold, used as the polymerisation inhibitor for vinyl aromatic compounds. 

Ethyl vinyl ether [109-92-2] M 72.1, b 35.5°, d4 0.755. It usually contains polymerisation inhibitors (usually amines, e.g. triethanolamine) which can be removed by fractional distillation. Redistil it from sodinm. [Beilstein 1IV 2049.] LACHRYMATORY. 

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