Pressure reactions under

Wallace C H, Rao L, Kim S-H, Heath J R, Nicol M and Kaner R B 1998 Solid-state metathesis reactions under pressure a rapid route to crystalline gallium nitride Appl. Phys. Lett. 72 596... 

The reaction of higher alkyl chlorides with tin metal at 235°C is not practical because of the thermal decomposition which occurs before the products can be removed from the reaction zone. The reaction temperature necessary for the formation of dimethyl tin dichloride can be lowered considerably by the use of certain catalysts. Quaternary ammonium and phosphonium iodides allow the reaction to proceed in good yield at 150—160°C (109). An improvement in the process involves the use of amine—stannic chloride complexes or mixtures of stannic chloride and a quaternary ammonium or phosphonium compound (110). Use of these catalysts is claimed to yield dimethyl tin dichloride containing less than 0.1 wt % trimethyl tin chloride. Catalyzed direct reactions under pressure are used commercially to manufacture dimethyl tin dichloride. 

Reactions under pressure are usually carried out in an autoclave. However, several simple vessels can be used for reactions at moderate pressure. A heavy walled Pyrex test tube or Kjeldahl flask drawn out and sealed with an oxygen torch makes a suitable container for many Diels-Alder reactions. The tube can be heated in an oil or water bath, but care must be exercised to protect against explosions. At the conclusion of the reaction, the tube is cooled to room temperature, the neck is scratched with a file or carborundum chip, and a hot Pyrex rod is touched to the scratch. A large crack in the neck should result, and the sealed top can be easily knocked off. 

Hydrogen fluoride is usually used in a large excess, recovered, and recycled. Because of its high vapor pressure at atmospheric pressure it is necessary to carry out the reaction under pressure in order to keep hydrogen fluoride in the liquid phase. 

Minimize energy demands such as heating, cooling and carrying out reactions under pressure exceeding 1 atm aim for reactions run under standard temperature and pressure conditions (room temperature and 1 atm). 

Ordinary laboratory apparatus cannot be used with gas from a cylinder for carrying out reactions under pressure in a closed system. For example, if it is desired to leave a reaction solution under pressure... 

Table 16 shows the results of the same reaction under different pressures between atmospheric pressure (10-4 GPa) to 0.78 GPa. At atmospheric pressure, nitro-group-substitution product, 18a, and o-mono- and p-monosubstitution products 19a and 20a were obtained in a total yield of 7.4% recovering 92% of the starting pentachloride 16. When the pressure was raised, the yields of these monosubstitution products increased at higher pressures di- and trisubstitution products appeared and this trend continued in the reactions under pressures above 0.60 GPa, affording higher yields of the trisubstitution product 23a. These results indicate that the second substitution occurred at the pressure... 

The present volume contains 13 chapters written by experts from 11 countries, and treats topics that were not covered, or that are complementary to topics covered in Volume 1. They include chapters on mass spectra and NMR, two chapters on photochemistry complementing an earlier chapter on synthetic application of the photochemistry of dienes and polyenes. Two chapters deal with intermolecular cyclization and with cycloadditions, and complement a chapter in Volume 1 on intramolecular cyclization, while the chapter on reactions of dienes in water and hydrogen-bonding environments deals partially with cycloaddition in unusual media and complements the earlier chapter on reactions under pressure. The chapters on nucleophiliic and electrophilic additions complements the earlier chapter on radical addition. The chapter on reduction complements the earlier ones on oxidation. Chapters on organometallic complexes, synthetic applications and rearrangement of dienes and polyenes are additional topics discussed. 

Phenolic resins. The oldest condensation reaction on record is between phenol and formaldehyde to produce phenolics. Professor Adolf von Baeyer first documented the reaction in 1872, for which the Nobel Committee awarded him their prize in 1905. Thirty years later, a technical application of this reaction was worked out by Dr. Leo Baekeland, when he showed that useful moldings can be made by carrying out the final stages of the reaction under pressure. As his reward, phenolic resins are still often called Bakelite, a seemingly better deal chan Baeyer s. At one time, phenolics were the workhorse of the plastics industry. 

Rathke and Feder have employed Co2(CO)8 as the catalyst precursor in their studies. Samples withdrawn from reactions under pressure were analyzed for both total cobalt and for HCo(CO)4 (35) conversion to HCo(CO)4 was observed to the extent of 50-90%, varying according to (14) with temperature and hydrogen pressure. Experiments with different levels of catalyst showed that the overall rate of CO reduction was first-order in the HCo(CO)4 concentration, as determined by titration of reaction samples. Thus, there is substantial evidence that the catalyst in this system (or more precisely, the species present in the transition state of the rate-determining catalytic step) is a mononuclear cobalt complex. The observed kinetic dependences [Eq. 

We studied the reaction under pressures about 10 2 mm Hg in a static... 

Hydrogenation under pressure. The following account refers primarily to commercial apparatus suitable for conducting hydrogenations under pressure the apparatus can of course be employed for other reactions under pressure (Section 2.17.2, p. 97), but some modifications of experimental procedure will then be necessary. 

Reactions under pressurized conditions are not illustrated in this book, although there are a number of pressurized reaction vessels made of ceramic and plastic materials provided by the manufactures of microwave equipment (see Section 3.4). These vessels should not be replaced under any conditions with other vessels and cannot be switched between different type of microwave reactors either. 

Figure 5.1. Reaction vessels for performing chemical reactions under pressurized conditions. Reprinted with the permission from [3].

In a flow-through reaction under pressure, the outlet of the reactor was attached to traps via a needle valve. The reactor was pressurized with 1.4 MPa of nitrogen, and the needle valve was closed. The alcohol mixture was pumped at 0.5 cm3/min for 15 min. The pressure inside the reactor increased to 1.8-2.1 MPa. The valve was slightly opened to allow the product to condense into two ice-cooled traps by maintaining the pressure inside the reactor. The run was continued for another 15 min. 

The reaction under pressure of ethanolamine and urea, preferably in excess ammonia, was investigated only briefly. It was found to proceed rapidly to produce yields of approximately 38%, based upon the alkanolamine, at 300° and about 900 atmospheres pressure. 

A convenient synthesis of phosphinines 185 involves the reaction of pyrylium salts 184 with either an excess of tris(trimethylsilyl)phosphine in acetonitrile, or alternatively with PH3 under pressure at 110°C <2001CEJ3106>. Better yields are often obtained using the direct reaction with PH3 (Equation 37). 2-t-Butyl phosphinines 187 can be prepared by reaction under pressure of /-butylphosphaacetylene with the a-pyrone 186 (Equation 38). 

This compound was first obtained by C. Claus1 as a light pink crystalline powder later it was described by W. Palmaer2 as pale yellow octahedral crystals. Palmaer s preparation starts from an iridium(III) chloride solution which is treated with concentrated aqueous ammonia. By carrying out the reaction under pressure in a sealed tube, the yield is substantially increased (up to 70%). 

The 1-1. centrifuge bottles (Coming No. 1280) carrying No. 6 rubber stoppers, as used for catalytic hydrogenation, are suitable for carrying out reactions under pressures up to at least 3 atmospheres. The submitter used a heavy, selected 2-1. round-bottomed flask instead of the four bottles specified in the procedure above. 

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