Potassium hydrogencarbonate

In one process the carbon dioxide is removed using potassium carbonate solution, potassium hydrogencarbonate being produced ... 

Some solids are either too soluble, or the solubility does not vary sufficiently with temperature, in a given solvent for direct crystallisation to be practicable. In many cases, the solid can be precipitated from, say, a concentrated aqueous solution by the addition of a liquid, miscible with water, in which it is less soluble. Ethanol, in which many inorganic compounds are almost insoluble, is generally used. Care must be taken that the amount of ethanol or other solvent added is not so large that the impurities are also precipitated. Potassium hydrogencarbonate and antimony potassium tartrate may be purified by this method. 

Tilak et described the use of excess mixed carbonic anhydrides to force condensation reactions to completion followed by the destruction of the excess mixed anhydride via the addition of aqueous potassium hydrogencarbonate. Hydrolysis of the nnixed anhydride was rapid and the resulting protected dipeptide could be extracted into ethyl acetate in a high state of purity, leaving the excess amino acid derivative and the salts in the aqueous phase. Without further purification the protected dipeptide was N -deprotected and reacted with the next mixed anhydride, and the process repeated until the desired peptide was obtained. Beyerman et al. substantially expanded the scope of this procedure and named it the REMA method for peptide synthesis (Repetitive Excess Mixed Anhydride).P°1 These reaction conditions provide an excellent method to ensure complete reaction of the amine component as well as rapid reaction rates and minimal side products. However, care must be taken to ensure that the excess carboxylic acid component is soluble in sodium hydrogencarbonate solution, e.g. when Z-Asp(OBzl)-OH is the acid component, it is extracted into the ethyl acetate as the sodium salt along with the product. With the due precautions the yields of small peptides are so high that the method could be applied without purification of the intermediate products, that is, in a repetitive way. 

The powdered alkali metal (K, Na etc.) phenoxide (ca.O.lg) was placed in a vial fLUed with carbon dioxide, and covered with parafihn. Carbon dioxide of purity more than 99.95% was supplied through a capillary tubing at room temperature. After the absorption of the gas, the weight increment was measured, and a portion of the sample was transferred in an nmr tube of 5 mm and dissolved in DMF with acetone-de, or in DMSO-d with addition of TMS. The nmr spectra on a JEOL-JNM GX 270 spectrometer were taken without delay. For the kinetic studies, a 150 mL aqueous solution containing resorcinol and potassium hydrogencarbonate was kept at 80 C with or without bubbling carbon dioxide, then an ahquot was taken at given time for nmr and/or HPLC analyses. ... 

The rate of the formation of /3 -resorcylic acid (RA) was a first order with respect both to ROH and to KHCOi. The overall reaction rate with bubbling carbon dioxide gas into the aqueous solution of potassium hydrogencarbonates is d[resorcylic acidj/dt = ki[resorcinol][KHCO,d + k2[resorcinol][pC02] ( 1)... 

The ki of the carboxylation of resorcinol with ammonium hydrogencarbonate was about one tenth of that with potassium hydrogencarbonate. These results are in agreement with the reported lower yield (53.9%) [7] of the product even at applying higher pressure (5 MPa) and higher temperatures (110-125 °C). 

Another example illustrating the safe operation of micro reactors at elevated temperatures and pressures was reported by Hessel et al. [25], for the industrially relevant Kolbe-Schmidt reaction (Scheme 6.8). Potassium hydrogencarbonate (31) was selected as a raw material as it is cheap and readily available, making it suitable for the industrial-scale preparation of 2,4-dihydroxybenzoic acid (32) water was selected as the reaction solvent as it is inexpensive (100-1000 lh-1). To optimize the continuous flow conditions, the authors employed a stainless-steel capillary reactor and evaluated the effect of pressure for a fixed reaction time of 6.5 min at 120 °C. 

Potassium chloride is reacted with carbon dioxide in precarbonated isopropylamine solution under pressure in an autoclave. Potassium hydrogencarbonate precipitates and the amine is converted into isopropylamine chlorohydrate. The potassium salt is isolated by filtration, washed free of amine and heated to convert it to the carbonate. Unreacted amine present in the filtrate is recovered by distillation. Hydrated lime is then added to convert the isopropylamine chlorohydrate back to the amine, which is also recovered by distillation. The main uses of potassium carbonate are the production of glass and sodium silicate. 

If the hydrolysis is conducted in the presence of aqueous potassium hydrogencarbonate a cyclic transition state may account for the product formation ( ). 

Potassium hydrogencarbonate, which is still used for standardization in acid-base titrations, was introduced by Than in 1860. The various redox tit-rants, their originators, and the dates are Hsted in Table 1. 

Sodium and potassium hydrogencarbonates are less soluble than the carbonates. Magnesium, calcium, strontium and barium hydrogencarbonates exist only in solution. Attempts to remove the water destroy the compounds ... 

---