Solvent reflux temperature

In case of complete malfunction of cooling and stirring systems, the temperature may exceed the solvent reflux temperature [34], Accordingly, a slow dosing of the methyl chloroformate is necessary to have control over the heat release. After having determined the reaction parameters at 1 g scale, the reaction was carried out in a microreactor with 91% yield at 7 min residence time. More than 1 kg of N-methoxycarbonyl-L-tert-leudne was prepared within 12 h. 

The coordination metal complexes are often air-sensitive, so preparations involving nonaqueous and inert solvents or vapor phase reactions (chemical vapor deposition (CVD), Section A.4.9) are required. The reactions are usually performed between room temperature and a maximum that is limited by the decomposition temperature of the precursor for vapor phase reactions, and the solvent reflux temperature for liquid phase reactions. 

A few authors have mentioned that the use of chloride metal complexes gives a reproducible amount of grafted metal Benvenutti et al. [34] for the grafting of SbCU on silica in CCI4 at the solvent-reflux temperature, Lindblad and Lindfors [36] for the grafting of WOCU on silica at 473 K, Haukka and Lakomaa [26] for the grafting of TiCU on silica at 450 K and 723 K. 

Formation of the alkene is thought to proceed via initial formation of a Ti-pinacolate followed by its deoxygenation to produce the double bond. In support of the proposed mechanistic scheme are the facts that (1) pinacol intermediates can be isolated when the coupling reaction is carried out at 0 °C rather than at solvent reflux temperature and (2) treatment of isolated pinacols with low-valent titanium at 60 °C deoxygenates them to the corresponding alkenes. 

Polyimides. The preparation of the polyimides proceeds through poly(amic acid) intermediates. The poly(amic acid) can be isolated providing the temperature of the condensation is properly controlled. At 50°C the structure formed is almost entirely poly(amic acid) while at the solvent reflux temperature almost 100% polyimide is formed. 

A crude yield of 90% was obtained in ether at —25 °C. When performed in a batch mode on 70 mg scale, no safety issues were taken and an 81% yield was obtained [42]. Reaction calorimetry reveals a very exothermic reaction after feeding and subsequent mixing with an initiation period that is, the response of the heat flow curve is delayed by about 1 min as compared to the feed curve (see Figure 11.6). Therefore, the heat release rate with this mode of addition is not feed controlled. The reaction is very sluggish, since the reaction occurs at a single blow as soon as 60% of the material has been added. Calculating the worsttemperature rise shows that the reaction would rapidly increase in temperature and can approach the solvent reflux temperature, possibly throwing out the reaction mixture in case of... 

McMurry reactions will be presented in the following order intermolecular, intramolecular, mixed (tandem) couplings of aldehydes and ketones, and finally keto ester, oxoamide, and acetal couplings. All the compounds which serve as illustrations are listed in Tables 6.1-6.10, along with the titanium reagents and solvents used for their preparation and the yields of isolated products where not specified, the reactions were performed at solvent reflux temperature. 

Initiators, usually from 0.02 to 2.0 wt % of the monomer of organic peroxides or azo compounds, are dissolved in the reaction solvents and fed separately to the kettie. Since oxygen is often an inhibitor of acryUc polymerizations, its presence is undesirable. When the polymerization is carried out below reflux temperatures, low oxygen levels are obtained by an initial purge with an inert gas such as carbon dioxide or nitrogen. A blanket of the inert gas is then maintained over the polymerization mixture. The duration of the polymerization is usually 24 h (95). 

Keta.Is, Trimethylpentanediol reportedly forms a cycHc ketal by heating it with benzophenone ia the presence of sulfonic acid catalysts at reflux temperatures ia toluene (64). These are said to be useful as aprotic solvents for ink-jet printing and as inflammation inhibitors for cosmetic preparations... 

Oxidation. Atmospheric oxidation of 1,2-dichloroethane at room or reflux temperatures generates some hydrogen chloride and results in solvent discoloration. A 48-h accelerated oxidation test at reflux temperatures gives only 0.006% hydrogen chloride (22). Addition of 0.1—0.2 wt. % of an amine, eg, diisopropylamine, protects the 1,2-dichloroethane against oxidative breakdown. Photooxidation in the presence of chlorine produces monochloroacetic acid and 1,1,2-trichloroethane (23). 

In a 500-ml. round-bottomed flask fitted with a reflux condenser are placed 16.2 g. (0.08 mole) of dry a-naphthylthiourea (Note 1) and 180 ml. of redistilled chlorobenzene. The flask is heated at the reflux temperature by means of an electric heating mantle. Evolution of ammonia begins almost at once, and all of the solid dissolves after 30-45 minutes. The solution is maintained at reflux for 8 hours (Note 2) and then evaporated on a steam bath at water-pump pressure to remove all of the chlorobenzene. The residue crystallizes on cooling and is extracted with four 30-ml. portions of boUing hexane (Note 3). Removal of solvent from the combined hexane extracts affords pale yellow crystals of naphthyl isothiocyanate, m.p. 58-59°. The yield is 12.7-13.0 g. (86-88%). Recrystallization from hexane (9 ml. of hexane for 1 g. of solute) gives colorless needles, melting point unchanged (Note 4). 

The van Leusen reaction forms 5-substituted oxazoles through the reaction of p-tolylsulfonylmethyl isocyanide (1, TosMIC) with aldehydes in protic solvents at refluxing temperatures. Thus 5-phenyloxazole (2) is prepared in 91% yield by reacting equimolar quantities of TosMIC and benzaldehyde with potassium carbonate in refluxing methanol for 2 hrs. ... 

The synthesis of flavones has also seen modifications over the years. One of the primary modifications has been substituting the carboxylate salt for other bases. Kohn and Low showed that catalytic amounts of triethylamine allowed for the reaction to be run at 160 Looker and coworkers expanded on the Kohn and Low modification by using amines as the solvent, and thus reduced the reaction temperatures. They typically found that the reaction could be run at the refluxing temperatures of the amine. They showcased this modification by converting oi-methoxyphloroacetophenone (35) to the methyl ether of galangin (36) using a variety of amines in 60-75% yield with benzoic anhydride. 

Cl Compound of Code No. CM 6912 25 g of the imine obtained under (B), dissolved in 400 ml of acetic acid, are heated at the reflux temperature for 1 hour. After evaporating the solvent in vacuo, the residue is taken up in methylene chloride. The solution is washed with a dilute sodium bicarbonate solution and then with water. After evaporating the solvent, the residue is chromatographed on silica, elution being carried out with an 80/20 mixture of ether and ethyl acetate. 9 g of benzodiazepine are thus obtained. Melting point 196. ... 

To a solution of 32 g of benzyl-t-butylamine in 300 ml of absolute ethanol at reflux temperature was added 32 g of 3,5-dibenzyloxy-C0bromoacetophenone in 10 ml of dry benzene. The mixture was refluxed for 20 hours and then evaporated. When absolute ether was added to the residue, benzyl-t-butylamine hydrobromide was precipitated. The precipitated compound was filtered off and to the filtrate was added an excess of 2N sulfuric acid. This caused precipitation of the hydrogen sulfate of 3.5-dibenzyloxy-60-(benzyI-t-butylamino)-acetophenone which was recrystallized from acetone/ether. If the product is crystallized from different organic solvents, the melting point will vary with the type and amou nt of solvent of crystallization, but the product can be used directly for hydrogenation. 

The auto-decomposition of lead tetraacetate in acetic acid, which normally occurs at reflux temperature , can be studied at 50 °C in the presence of sodium acetate The principal products of both the uncatalysed and catalysed decompositions are acetoxyacetic acid and carbon dioxide. The kinetic order of the normal decay of Pb(IV) is complex and evidence was obtained that oxidation of products is significant after the earliest stages. The evidence indicates that slow, simple homolytic breakage of lead tetraacetate to give Pb(OAc)3- and AcO-does not occur but that the solvent plays an integral part, e.g. 

---