Intermittent heating

It may be mentioned that diazonium fluoborates containing the nitro group usually decompose suddenly and with violence upon heating, hence if o- or p-fluonitrobenzene are required, the fluoborates (in 10-20 g. quantities) should he mixed with 3-4 times their weight of pure dry sand (or barium sulphate or sodium fluoride) and heated cautiously until decomposition commences intermittent heating will be required to complete the reaction. 

If the reaction becomes too vigorous, it may be necessary to cool the flask by covering it with a damp cloth. Normally the decomposition proceeds smoothly under the intermittent heating. If the salt is damp, the reaction may proceed more vigorously and unless the flask is cooled, it may pass beyond control. 

High output rate relative to size. intermittent heating ... 

In an utmost simplistic approach, an unmodified household microwave oven has been used in this study with excellent results and the generation of higher temperatures is simply avoided by intermittent heating [35]. 

Solid-state synthesis of /J-nitrostyrenes has been reported by Varma et al. in a process that uses readily available styrene and its substituted derivatives and inexpensive clay-supported nitrate salts, clayfen and clayan (Scheme 6.50) [170], In a simple experiment, admixed styrene with clayfen or clayan is irradiated in a MW oven (-100-110 °C, 3 min) or heated in an oil bath (-100-110 °C, 15 min). For clayan intermittent heating is recommended with 30-s intervals to maintain the temperature below 60-70 °C. Remarkably, the reaction proceeds only in solid state and leads to the formation of polymeric products in organic solvent. 

The mixture is heated cautiously on a hot plate to avoid excess frothing. When the frothing has almost subsided, additional concentrated nitric add is added, 90 g. (65 ml., 1.0 mole) at a time, with swirling and intermittent heating to control the vigorous reaction. The solid changes from gray-black to a cream color after six 90-g. portions of concentrated nitric acid have been used. 

Bhuiyan, M.T.R., Hirai, N. and Sobue, N. (2001). Effect of intermittent heat treatment on crystallinity in wood cellulose. Journal of Wood Science, 47(5), 336-341. 

The second example of the use of the intermittent heating is for identifying centromeres in gastric cancer cells (Kitayama et al., 1999). A panel of 17 centromeric specific a-satellite probes was used for detecting chromosomal instability in these cells. The study of centromeres is important because chromosomal abnormalities are a well-known characteristic of human cancers. 

The crude 5-amino-N-methylisophthalamic acid was dissolved in hydrochloric acid (100 ml concentrated acid and 100 ml of water) and this solution was diluted to 1 liter with water. Iodine monochloride (27.4 g of 95% ICI, 0.16 mole) in concentrated hydrochloric acid (30 ml) was added in one portion to the stirred solution maintained at 54°C. The solution was heated on a steam bath. After 2 hours the solution was diluted to 1.5 liters and after 3 hours titration of an aliquot indicated that 50% of the iodine monochloride had been consumed. Precipitation of a solid began after 33/4 hours of reaction (75°C). Intermittent heating and stirring was continued for 4 days, 10 g of 95% iodine monochloride was added during the third day. After 4 days, titration of an aliquot indicated that 96% of the theoretical quantity of iodine monochloride had been consumed. The precipitated solid was filtered off, washed with water and dried at 75°C under reduced pressure. Yield of 5-amino-2,4,6-triiodo-N-... 

Two variations have been described. In the cyclic route, a chequerbrick surface is intermittently heated by combustion of natural gas with air followed by the introduction of natural gas alone for reaction, until the... 

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