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In the present work, we have studied the effect of ammonia and formic acid on the kinetic stability of sulfurous acid using high level ab initio calculations. Our investigation reveals that the decomposition reaction of sulfurous acid becomes barrierless in the presence of both ammonia and formic acid. The half-life of the isolated sulfurous acid is estimated to be ∼20 days at room temperature, which becomes only ∼4.0 × 10-3 s and ∼7.08 × 102 s in the presence of ammonia and formic acid, respectively. These results indicate that, in the presence of ammonia, the stability of sulfurous acid reduces substantially at room temperature. The temperature dependency of the rate constant values indicates that, in the presence of ammonia and formic acid, the reaction has a negative activation energy, while the uncatalyzed and water catalyzed channels have a positive activation energy. We have also studied the pressure dependency of the catalyzed reaction, which suggests that the ammonia catalyzed channel is most sensitive towards the pressure change, as the values of the bimolecular rate constant (kbi) for this channel were found to be increased by an order of magnitude on going from 0.1 to 10 atm of pressure. Whereas, for the FA and WM catalyzed channels the changes in kbi with pressure were negligible.

The ion corresponding to protonated sulfurous acid, H3SO3(+), has been successfully delivered into the gas phase by electrospray ionization of the solution of a suitable precursor and an in-source fragmentation process. The neutral acid is a highly elusive molecule. However, its gas-phase basicity has been ascertained by means of a kinetic study of proton-transfer reactivity. The structure of the H3SO3(+) sampled ion has been probed by IRMPD spectroscopy in two complementary IR frequency ranges in conjunction with density functional theory calculations and found to conform to a trihydroxosulfonium ion. The characteristic IR signatures may aid in deciphering the presence of this species in extraterrestrial atmospheres.

Herein, theoretical studies were performed on the atmospheric oxidation of sulfurous acid (H2SO3) and sulfite ions (HSO3−) by ozone (O3) to produce sulfuric acid and hydrosulfate ions. The most favorable path for the H2SO3 + O3 reaction has been found to be initiated from concerted H-abstraction and oxygen addition, with an overall energy barrier of 18.3 kcal mol−1. On the other hand, the most favorable path for the HSO3− + O3 reaction is initiated from oxygen addition, with an overall energy barrier of only 0.3 kcal mol−1. Kinetic simulations were performed to estimate the significance of these reactions in the formation of atmospheric sulfate and destruction of the ozone layer. The results provide new insight into the missing source of atmospheric sulfate and particulate matter.

The conditions (solid to liquid ratio, acid concentration, temperature, process duration) were selected for the effective high-temperature pretreatment of corn cobs with dilute sulfurous acid. The activity of the enzymatic complexes «CellicCTec2» and «CellicHTec2» of the company «Novozymes» in the process of corn cobs hydrolysis was studied. The maximum yield of reducing sugars was 45 % of absolutely dry substance at a concentration of the enzymatic preparation «CellicCTec2» 3 % (of corn cobs absolutely dry substance) and solid to liquid ratio 1:30. The total amount of extracted reducing substances is 66 % of the theoretical yield of carbohydrates in the corn cobs.

Acidic tropospheric aerosols contain inorganic species such as sulfurous acid (H(2)SO(3)). As the main alkaline species, ammonia (NH(3)) plays an important role in the heterogeneous neutralization of these acidic aerosols. An aerosol flow-tube apparatus was used to obtain simultaneous optical and size distribution measurements using FTIR and SMPS measurements, respectively, as a function of relative humidity and aerosol chemical composition. A novel chemiluminescence apparatus was also used to measure ammonium ion concentration [NH(4)(+)]. The interactions between ammonia and hydrated sulfur dioxide (SO(2)·H(2)O) were studied at different humidities and concentrations. SO(2)·H(2)O is an important species as it represents the first intermediate in the overall atmospheric oxidation process of sulfur dioxide to sulfuric acid (H(2)SO(4)). This complex was produced within gaseous, aqueous, and aerosol SO(2) systems. The addition of ammonia gave mainly hydrogen sulfite (SHO(3)(-)) tautomers and disulfite ions (S(2)O(5)(2-)). These species were prevalent at high humidities enhancing the aqueous nature of sulfur(IV) species. Their weak acidity is evident due to the low [NH(4)(+)] produced. Size distributions obtained correlated well with the various stages of particulate compositional development.

Sulfurous acid was used for pretreatment of sugar beet pulp (SBP) in order to achieve high efficiency of both extraction of carbohydrates and subsequent enzymatic hydrolysis of the remaining solids. The main advantage of sulfurous acid usage as pretreatment agent is the possibility of its regeneration. Application of sulfurous acid as hydrolyzing agent in relatively low concentrations (0.6-1.0 %) during a short period of time (10-20 min) and low solid to liquid ratio (1:3, 1:6) allowed effective extraction of carbohydrates from SBP and provided positive effect on subsequent enzymatic hydrolysis. The highest obtained concentration of reducing substances (RS) in hydrolysates was 8.5 %; up to 33.6 % of all carbohydrates present in SBP could be extracted. The major obtained monosaccharides were arabinose and glucose (9.4 and 7.3 g/l, respectively). Pretreatment of SBP with sulfurous acid increased 4.6 times the yield of glucose during subsequent enzymatic hydrolysis of remaining solids with cellulase cocktail, as compared to the untreated SBP. Total yield of glucose during SBP pretreatment and subsequent enzymatic hydrolysis amounted to 89.4 % of the theoretical yield. The approach can be applied directly to the wet SBP. Hydrolysis of sugar beet pulp with sulfurous acid is recommended for obtaining of individual monosaccharides, as well as nutritional media.

The characterization and isolation of sulfurous acid (H2SO3) have never been accomplished and thus still remain one of the greatest open challenges of inorganic chemistry. It is known that H2SO3 is thermodynamically unstable. In this study, however, we show that a Ci-symmetric dimer of sulfurous acid (H2SO3)2 is 3.5 kcal mol-1 more stable than its dissociation products SO2 and H2O at 77 K. Additionally, we have investigated the kinetic stability of the sulfurous acid monomer with respect to dissociation into SO2 and H2O and the kinetic isotope effect (KIE) on this reaction by transition-state theory. At 77 K, the half-life of H2SO3 is 15 x 10(9) years, but for the deuterated molecule (D2SO3) it increases to 7.9 x 10(26) years. At room temperature, the half-life of sulfurous acid is only 24 hours; however, a KIE of 3.2 x 10(4) increases it to a remarkable 90 years. Water is an efficient catalyst for the dissociation reaction since it reduces the reaction barrier tremendously. With the aid of two water molecules, one can observe a change in the reaction mechanism for sulfurous acid decomposition with increasing temperature. The most likely mechanism below 170 K is via an eight-membered transition-state ring; yet, above 170 K, a mechanism with a six-membered transition state ring becomes the predominant one. For deuterated sulfurous acid, this change in reaction mechanism can be observed at 120 K. Consequently, between 120 and 170 K, different predominant reaction mechanisms occur for the decomposition of normal and deuterated sulfurous acid when assisted by two water molecules. However, the much longer half-life of deuterated sulfurous acid and the stability of the sulfurous acid dimer at 77 K are encouraging for future synthesis and characterization under laboratory conditions.

The individual as well as the synergistic effect of depolarisers, such as H2SO3 (aq) and/or Fe2+ (aq) and/or Co2+ (aq) on copper electrodeposition has been studied. A comparison is made of their relative effects on anode potential, cell potential, current efficiency (CE), power consumption and deposit quality. Linear sweep voltammetry (LSV) has been used to study the cathodic and the anodic behaviours of the depolarisers during electrodeposition of copper. The lowest value in anode potential is observed in the presence of H2SO3 and Fe2+ (aq) together. The presence of either added Fe2+ (aq) or added Co2+ (aq) or both together polarises the cathode deposition potential of copper; the extent of polarisation is more prominent in the presence of only Fe2+ (aq). In contrast, the cathode deposition potential of copper is depolarised in the presence of H2SO3 in the electrolyte; the depolarisation increases when Fe2+ (aq) is added to the electrolyte containing sulfurous acid. X-ray diffraction data show the change in the relative growth on the preferred orientations of cathode copper deposits in the absence and the presence of H2SO3 (aq) and/or Fe2+ (aq) and/or Co2+ (aq) in the electrolyte solution. Scanning electron microscopy (SEM) results establish different surface morphology of the copper samples deposited in the presence of H2SO3/Fe2+ (aq)/Co2+ (aq)/Fe2+ (aq)+Co2+ (aq)/H2SO3+Fe2+ (aq)/H2SO3+Co2+ (aq)/H2SO3+Fe2+ (aq)+Co2+ (aq) in the electrolyte solution.

The potential of sulfurous acid prehydrolysis followed by chemical pulping was examined at the laboratory scale using radiata pine. The residue obtained by sulfurous acid prehydrolysis with base addition was sufficiently delignified in a subsequent soda pulping stage, while the delignification of the residue was completely insufficient in subsequent kraft pulping. The residues prepared by prehydrolyses of hydrochloric and sulfuric acids were not delignified sufficiently regardless of the pulping method. The yield of hemicellulose-derived monosaccharides was about 90% on a theoretical basis in the optimal sulfurous acid prehydrolysis. In subsequent soda pulping under various conditions, pulps with kappa number 21 to 34, pulp yield 37 to 41%, and high cellulose content could be prepared from the residue obtained by sulfurous acid prehydrolysis with base addition. It was suggested from these results that sulfurous acid prehydrolysis with base addition in combination with subsequent soda pulping is an effective method for the utilization of wood hemicelluloses.

The effect of esters of sulfurous acid as primary antioxidants was examined. Different aliphatic, aromatic, open-chain and cyclic sulfites were synthesized. The reactions of organic sulfites with RO 2 and RO radicals, the chain carriers of the autoxidation of hydrocarbons and polymers, were simulated by means of the thermal decomposition of azobisisobutyronitrile (AIBN) in the presence of oxygen and of di-tert-butylperoxalate (DTBPO). The reactivity of organic sulfites with 2-cyanoisopropylperoxyl radicals is low. Only aromatic sulfites are able to trap peroxyl radicals; however, they are not very effective primary antioxidants. The reactions of the organic sulfites with tert-butoxyl radicals generally lead to an increase in the rate of decomposition of DTBPO, as determined from rate constants measured at 50 °C. A decomposition of DTBPO induced by liberated tert-butyl radicals in the presence of alkyl sulfites is very probable. Alkyl sulfites and aromatic sulfites with aliphatic groups act mainly as hydrogen donors in reactions with alkoxyl and peroxyl radicals.

Oxidation of sulfurous acid (H2SO3) to sulfuric acid (H2SO4) by dissolved oxygen (O2) in an aqueous solution was remarkably enhanced by freezing. The concentration of sulfurous acid in a sample solution which froze in a −10 °C refrigerant for 60 min decreased by about 50%, and three freeze/thaw cycles resulted in perfect conversion into sulfuric acid. The difference of reaction rates in −20 °C and −10 °C refrigerants indicated that the rate-determining step of the reaction was the growth rate of ice formation in the sulfurous acid in an aqueous solution. The yield of sulfurous acid oxidation in a −10 °C refrigerant was higher than that in a −20 °C refrigerant.

The oxidation of sulfite by Thiobacillus thiooxidans was studied at various pH values with changing concentrations of potassium sulfite. The optimal pH for sulfite oxidation by cells was a function of sulfite concentrations, rising with increasing substrate concentrations, while that by the cell extracts was unaffected. The sulfite oxidation by cells was inhibited at high sulfite concentrations, particularly at low pH values. The results from kinetic studies show that the fully protonated form of sulfite, sulfurous acid or sulfur dioxide, is the form which penetrates the cells for the oxidation.