Bicarbonate dehydration

Pocket, Y. and D. W. Bjorkquist (1977) Stopped-flow studies of carbon dioxide hydration and bicarbonate dehydration in H2O and D2O. Acid-base and metal ion catalysis./. Am. Chem. Soc. 99, 6537-43. 

Examination of the rate of bicarbonate dehydration reactivity of [([12]aneN3)Zn-(0H2)](C104)2 as a function of zinc complex concentration and pH revealed that this reaction is only slightly catalyzed by the aqua (Zn-OH2) form of the complex. A proposed mechanism for bicarbonate dehydration is shown in Scheme 3. Once again, the kinetically determined pKa value matched well with that determined for [([12]aneN3)Zn(0H2)](C104)2, indicating the validity of the proposed mechanism. 

Overall, [([12]aneN3)Zn(0H2)](C104)2 exhibits pH-dependent catalytic behavior for the hydration of C02 and dehydration of HCO. The rate-determining step of the C02 hydration reaction is the uptake of C02 by the zinc hydroxide complex. The rate-determining step in bicarbonate dehydration is substitution of the labile zinc-bound water molecule by the bicarbonate anion. The overall catalytic mechanism for both reactions is shown in Scheme 4. In considering this mechanism, it is... 

Complexes [Co(X)(Tpph)(CH30H)m]- CH30H (X = N3, m = 1, n = 2 X = NCS, m = 0, n = 0) have been synthesized and used as catalysts in the bicarbonate dehydration reaction. The coordination geometries of these Co(II) complexes in solution are five-coordinated trigonal bipyramidal as revealed by the spectroscopic... 

Mutations in conserved regions of the 86, 96 protein did not affect the highly proficient native activity despite the absence of a purifying selection for bicarbonate dehydration. 

The cmde phthaUc anhydride is subjected to a thermal pretreatment or heat soak at atmospheric pressure to complete dehydration of traces of phthahc acid and to convert color bodies to higher boiling compounds that can be removed by distillation. The addition of chemicals during the heat soak promotes condensation reactions and shortens the time required for them. Use of potassium hydroxide and sodium nitrate, carbonate, bicarbonate, sulfate, or borate has been patented (30). Purification is by continuous vacuum distillation, as shown by two columns in Figure 1. The most troublesome impurity is phthahde (l(3)-isobenzofuranone), which is stmcturaHy similar to phthahc anhydride. Reactor and recovery conditions must be carefully chosen to minimize phthahde contamination (31). Phthahde [87-41-2] is also reduced by adding potassium hydroxide during the heat soak (30). 

Figure 6-9. The Bohr effect. Carbon dioxide generated in peripheral tissues combines with water to form carbonic acid, which dissociates into protons and bicarbonate ions. Deoxyhemoglobin acts as a buffer by binding protons and delivering them to the lungs. In the lungs, the uptake of oxygen by hemoglobin releases protons that combine with bicarbonate ion, forming carbonic acid, which when dehydrated by carbonic anhydrase becomes carbon dioxide, which then is exhaled.

This isotonic volume expander contains sodium, potassium, chloride, and lactate that approximates the fluid and electrolyte composition of the blood. Ringer s lactate (also known as lactated Ringer s or LR) provides ECF replacement and is most often used in the perioperative setting, and for patients with lower GI fluid losses, burns, or dehydration. The lactate component of LR works as a buffer to increase the pH. Large volumes of LR may cause metabolic alkalosis. Because patients with significant liver disease are unable to metabolize lactate sufficiently, Ringer s lactate administration in this population may lead to accumulation of lactate with iatrogenic lactic acidosis. The lactate is not metabolized to bicarbonate in the presence of liver disease and lactic acid can result. 

CO3 species was formed and the X-ray structure solved. It is thought that the carbonate species forms on reaction with water, which was problematic in the selected strategy, as water was produced in the formation of the dialkyl carbonates. Other problems included compound solubility and the stability of the monoalkyl carbonate complex. Van Eldik and co-workers also carried out a detailed kinetic study of the hydration of carbon dioxide and the dehydration of bicarbonate both in the presence and absence of the zinc complex of 1,5,9-triazacyclododecane (12[ane]N3). The zinc hydroxo form is shown to catalyze the hydration reaction and only the aquo complex catalyzes the dehydration of bicarbonate. Kinetic data including second order rate constants were discussed in reference to other model systems and the enzyme carbonic anhy-drase.459 The zinc complex of the tetraamine 1,4,7,10-tetraazacyclododecane (cyclen) was also studied as a catalyst for these reactions in aqueous solution and comparison of activity suggests formation of a bidentate bicarbonate intermediate inhibits the catalytic activity. Van Eldik concludes that a unidentate bicarbonate intermediate is most likely to the active species in the enzyme carbonic anhydrase.460... 

The most fundamental process dealing with the activation of C02 involves the hydration of C02 to produce bicarbonate and the reverse dehydration of bicarbonate to produce C02. These processes are of biological and environmental significance since they control the transport and equilibrium behavior of C02. The spontaneous hydration of C02 and dehydration of HCO3 are processes that are too slow and must therefore be catalyzed by metal complexes in order to expedite the overall conversion rate. In biological systems, a series of enzymes, the carbonic anhydrases, are the efficient catalysts and can accelerate the reactions by up to 7 orders of magnitude. The mechanism of this... 

Metabolic acidosis In severe renal disease uncontrolled diabetes circulatory insufficiency due to shock, anoxia, or severe dehydration extracorporeal circulation of blood cardiac arrest and severe primary lactic acidosis where a rapid increase in plasma total CO2 content is crucial. Treat metabolic acidosis in addition to measures designed to control the cause of the acidosis. Because an appreciable time interval may elapse before all ancillary effects occur, bicarbonate therapy is indicated to minimize risks inherent to acidosis itself. 

Carbonic Anhydrase (MW2 = 30,000, 1 Zn) This enzyme occurs in red blood cells and catalyse the dehydration of bicarbonate ion and hydration of CO2. 

Acid-base and electrolyte balance High therapeutic dose especially when used in rheumatic fever, stimulates respiration and causes respiratory alkalosis. Reduction in bicarbonate and potassium level reduces the buffering capacity of the extracellular and intracellular fluid. Hypokalemia may lead to dehydration and hypernatremia. They also interfere with carbohydrate metabolism resulting in accumulation of pyruvic acid and lactic acid. 

Scaife (Ref 4). Blatt (Ref 3) lists a method of prepn from l-chloro-2-nitroethane and Na bicarbonate in 76% yield, developed during WWII in USA. Mom a (Ref 5) prepd the polymer from Nitromethane and formaldehyde thru intermediate formation of Nitroedianol, followed by dehydration with H3PO3 catalyst... 

Metabolic acidosis follows, and an increased anion gap results from accumulation of lactate as well as excretion of bicarbonate by the kidney to compensate for respiratory alkalosis. Arterial blood gas testing often reveals this mixed respiratory alkalosis and metabolic acidosis. Body temperature may be elevated owing to uncoupling of oxidative phosphorylation. Severe hyperthermia may occur in serious cases. Vomiting and hyperpnea as well as hyperthermia contribute to fluid loss and dehydration. With very severe poisoning, profound metabolic acidosis, seizures, coma. 

Potassium carbonate is used in the chemical industry as a source of inorganic potassium salts (potassium silicates, potassium bicarbonate), which are used in fertilizers, soaps, adhesives, dehydrating agents, dyes, and pharmaceuticals. Potassium carbonate used to make potassium lye produces soft soaps, which are liquids or semisolids rather than solids. Other uses of potassium carbonate includes use as a fire suppressant in extinguishers, as a C02 absorbent for chemical processes and pollution control, an antioxidant in rubber additives, and in pharmaceutical formulations. 

---