Aqueous Acid Hydrolysis Research Articles

Comparative study on liquid versus gas phase hydrochloric acid hydrolysis for microcrystalline cellulose isolation from sugarcane bagasse

Microcrystalline cellulose (MCC) was successfully synthesized from sugarcane bagasse using a rapid, low-temperature hydrochloric acid (HCl) gas treatment. The primary aim was to develop an energy-efficient “green” cellulose extraction process. Response surface methodology optimized the liquid-phase hydrolysis conditions to 3.3 % HCl at 117 °C for 127 min to obtain MCC with 350 degree of polymerization. An alternative gas-phase approach utilizing gaseous HCl diluted in hot 40 °C air was proposed to accelerate MCC production. The cellulose pulp was moistened to 15–18 % moisture content and then exposed to HCl gas, which was absorbed by the moisture in the cellulose fibers to generate a highly concentrated acidic solution that hydrolyzed the cellulose. The cellulose pulp was isolated from depithed bagasse through soda pulping, multistage bleaching and cold alkali purification. Hydrolysis was conducted by saturating the moist cellulose fibers with gaseous HCl mixed with hot air. Extensive analytical characterization using FT-IR, XRD, SEM, TGA, DSC, particle size, and porosity analyses verified comparable physicochemical attributes between MCC samples prepared via liquid and gas phase methods. The gas-produced MCC revealed 85% crystallinity, 71 Å crystallite dimensions, and thermally stable rod-shaped morphology with an average diameter below 200 μm. The similar material properties validate the proposed gas-based technique as an equally effective yet more energy-efficient alternative to conventional aqueous acid hydrolysis for fabricating highly pure MCC powders from lignocellulose. This sustainable approach enables the value-addition of sugarcane bagasse agro-industrial residue into cellulosic nanomaterials for wide-ranging industrial applications. In summary, the key achievements of this work are rapid MCC production under mild temperatures using HCl gas, optimization of liquid phase hydrolysis, successful demonstration of gas phase method, and extensive characterization verifying equivalence between both protocols. The gas methodology offers a greener cellulose extraction process from biomass.

Cover Feature: Gamma Radiation‐Induced Degradation of Acetohydroxamic Acid (AHA) in Aqueous Nitrate and Nitric Acid Solutions Evaluated by Multiscale Modelling (ChemPhysChem 5/2023)

The Cover Feature represents acetohydroxamic acid degradation in used nuclear fuel reprocessing cycles, where it is broken down by hydrolysis and radiation in aqueous nitric acid to form acetic acid, hydroxylamine, nitrous oxide, and hydrogen gas. Designed by Rett Longmore. More information can be found in the Research Article by Jacy K. Conrad, Gregory P. Horne and co-workers.

Degradation of amoxicillin applying photo-Fenton and acid hydrolysis processes with toxicity evaluation via antimicrobial susceptibility tests

ABSTARCT The antibiotic amoxicillin (AMX) is a semisynthetic aminopenicillin, classified as an β-lactam antibiotic. This work aims to evaluate the AMX degradation (190 mg L–1), in aqueous medium, applying photo-Fenton ([TOC]0 = 100 mgC L−1; FH2O2 = 3.27 mmol min−1; [Fe2+] = 0.27 mmol L−1; pH = 3.0; T = 40°C) and acid hydrolysis processes. Along the experiments, samples were withdrawn and analyzed by a total organic carbon (TOC) analyzer and a liquid chromatography system coupled to diode array (HPLC-DAD) and mass spectrometry (HPLC-MS) detectors. The hydrolysis process proved to be less efficient, because AMX removals greater than 80% were observed only after 24 hours of reaction (pH 2). Conversely, the photo-Fenton process removed completely AMX in just 20 minutes, reaching 85% of TOC removal in 2 hours. Finally, the AMX aqueous solutions treated by the studied processes was also evaluated in respect of its toxicity to some microorganisms, applying two antimicrobial susceptibility tests: disk-diffusion and broth microdilution methods. It was observed that the AMX aqueous solutions, pretreated by the photo-Fenton process, for just 7.5 min of reaction time, did not inhibit the microorganisms growth. The obtained results show that the photo-Fenton process was able to degrade AMX, in a relatively short time, and that the generated degradation products did not inhibit the microorganisms growth, when compared to acid hydrolysis process. Thus, it was verified the potential application of the photo-Fenton system as a pretreatment step to conventional biological oxidation processes for the treatment of industrial wastewaters.

Evaluation and Comparison of the Antioxidant Activity of Extractable Polyphenols and Non-extractable Polyphenols of Sour Orange Peel

Background and Objectives Research on food polyphenols has experienced a huge development during the last century. Most studies on polyphenolic compounds have focused on extractable polyphenols (EPP). However, an important polyphenolic fraction is ignored (Non-Extractable polyphenols (NEPP)) because they are trapped in the corresponding extraction residues. In this study, the antioxidant EPP and NEPP of sour orange peel, extracted by aqueous solvent and acid hydrolysis (with two different solvent systems) respectively, are evaluated and compared. Methods Antioxidant activity was evaluated by four tests of radical inhibition of 2, 2-diphenyl-1-picrylhydrazyl (DPPH), 2, 2-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP) and iron chelating. The amount of polyphenolic compounds, flavonoids, oligomeric proanthocyanidins, and flavanones were respectively determined by folin-ciocalteu, Aluminium chloride (AlCl3) and Ultraviolet–visible spectroscopy (UV-visible). Also, the anti-lipid peroxidation effect in rat liver was measured. Results The results of antioxidant analysis showed that NEPP with methanol/Sulfuric Acid Solvent had the highest level of antioxidant activity in sour orange peel. It can be due to the high polyphenolic compounds in this extraction compared to the others. Conclusion All extracts had antioxidant activity and can be suggested as a potential natural source in food and pharmaceutical industries.

Production and Properties of Microbial Polyhydroxyalkanoates Synthesized from Hydrolysates of Jerusalem Artichoke Tubers and Vegetative Biomass.

One of the major challenges in PHA biotechnology is optimization of biotechnological processes of the entire synthesis, mainly by using new inexpensive carbon substrates. A promising substrate for PHA synthesis may be the sugars extracted from the Jerusalem artichoke. In the present study, hydrolysates of Jerusalem artichoke (JA) tubers and vegetative biomass were produced and used as carbon substrate for PHA synthesis. The hydrolysis procedure (the combination of aqueous extraction and acid hydrolysis, process temperature and duration) influenced the content of reducing substances (RS), monosaccharide contents, and the fructose/glucose ratio. All types of hydrolysates tested as substrates for cultivation of three strains—C. necator B-10646 and R. eutropha B 5786 and B 8562—were suitable for PHA synthesis, producing different biomass concentrations and polymer contents. The most productive process, conducted in 12-L fermenters, was achieved on hydrolysates of JA tubers (X = 66.9 g/L, 82% PHA) and vegetative biomass (55.1 g/L and 62% PHA) produced by aqueous extraction of sugars at 80 °C followed by acid hydrolysis at 60 °C, using the most productive strain, C. necator B-10646. The effects of JA hydrolysates on physicochemical properties of PHAs were studied for the first time. P(3HB) specimens synthesized from the JA hydrolysates, regardless of the source (tubers or vegetative biomass), hydrolysis conditions, and PHA producing strain employed, exhibited the 100–120 °C difference between the Tmelt and Tdegr, prevailing of the crystalline phase over the amorphous one (Cx between 69 and 75%), and variations in weight average molecular weight (409–480) kDa. Supplementation of the culture medium of C. necator B-10646 grown on JA hydrolysates with potassium valerate and ε-caprolactone resulted in the synthesis of P(3HB-co-3HV) and P(3HB-co-4HB) copolymers that had decreased degrees of crystallinity and molecular weights, which influenced the porosity and surface roughness of polymer films prepared from them. The study shows that JA hydrolysates used as carbon source enabled productive synthesis of PHAs, comparable to synthesis from pure sugars. The next step is to scale up PHA synthesis from JA hydrolysates and conduct the feasibility study. The present study contributes to the solution of the critical problem of PHA biotechnology—finding widely available and inexpensive substrates.

Measurement of selenomethionine and selenocysteine in fish tissues using HPLC-ICP-MS

The extraction and measurement of selenomethionine (SeMet) and selenocysteine (SeCys) in fish muscle and liver tissues were evaluated. Preliminary experiments were undertaken with marine certified reference materials. NRCC TORT 1/2 Lobster hepatopancreas, NRCC DOLT 2/3; Dogfish liver and NIST 1566 a/b Oyster tissue were extracted using aqueous leaching, enzymatic hydrolysis and acid hydrolysis with ultrasound, microwave assisted heating and conventional heating using a hybridisation oven. High Se recoveries were obtained with the use of methanesulfonic acid as an extractant (89–92%); however, the low pH required for extraction is not compatible with most HPLC columns and dilution is required to analyse extracts that precluded the measurement of Se in samples from relatively uncontaminated environments. As well, Se species (SeMet and SeCys) degrade with the use of highly acidic extractants. Enzymatic hydrolysis with protease type XIV gave good recoveries (63–67%), but only SeMet was stable in the extract. As SeCys was not stable, a derivatisation step using iodoacetamide to form a stable carboxymethylated complex was used prior to enzymatic hydrolysis. Conventional heating at 37°C for 20h and microwave assisted heating at 45°C for 45min gave similar recoveries for CRMs but conventional heating gave slightly better recoveries for fish tissues.Two separate complementary methods were developed for the measurement of SeMet and SeCys in marine fish tissues; SeMet was measured after protease XIV hydrolysis and analysis using anion or cation exchange chromatography-ICPMS, while for the measurement of SeCys a carbamidomethylation derivatisation procedure prior to the protease hydrolysis was used and the separation of the species was carried out using size exclusion chromatography, followed by C8 ion-pair reversed-phase chromatography with ICPMS. Recoveries of SeMet and SeCys added to CRMs and fish tissues were 97±9% and 84±9% respectively.

The effect of manganese(II) chloride as a co-catalyst on cellobiose hydrolysis in dilute aqueous sulfuric acid and acidic ionic liquid mediums

The effects of adding MnCl2 as a co-catalyst on cellobiose hydrolysis in 0.016M aqueous H2SO4 and 0.032M 1-(1-propylsulfonic)-3-methylimidazolium chloride acidic ionic liquid mediums were studied at 60–90°C by measuring the glucose yields. The addition of MnCl2 produced enhancements in glucose yields in both aqueous acid mediums. The yield enhancements are highest at 60°C and gradually decrease at higher temperatures, suggesting that a weak interaction of MnCl2 with cellobiose causes the co-catalytic effect. FT-IR studies in the solid-state suggest that MnCl2 interacts with hydroxyl groups of cellobiose without causing significant changes in the pyranose ring conformations.

Approach to the synthesis of 8-nitroquinoline-2-carboxylic acid in high yield

A synthesis of 8-nitroquinoline-2-carboxylic acid was optimized, using the following basic scheme of transformations: 1) nitration of 2-methylquinoline with subsequent separation of a mixture of isomeric 8-nitroand 5-nitro-2-methylquinolines; 2) oxidation of the methyl group in 2-methyl-8-nitroquinoline (including consecutive steps of bromination and hydrolysis in aqueous sulfuric acid). A new method for the separation of isomeric 8-nitroand 5-nitro-2methylquinolines was suggested. The optimal conditions for the final step of hydrolysis were selected, which gave almost quantitative yield of 8-nitroquinoline-2-carboxylic acid.

Molecular labels for analysis of amines and diols by spray based ionization-mass spectrometry.

A family of imidazolium and pyridinium salts was synthesized for the purpose of labeling amines and 1,2-diols for highly sensitivite analysis by mass spectrometry. The chosen mass labels are shown to serve as effective reporters when bound to particles functionalized with amines or 1,2-diols and the binding is reversible. The straightforward synthetic route allows analogous internal standards to be generated quickly. Solvents amenable to electrospray ionization facilitate the rapid liberation of imidazolium and pyridinium mass labels from particles by hydrolysis in aqueous acid, while the acetal bond remains stable in anhydrous or buffered aqueous solution. Detection of the labels is demonstrated at 1 nM and quantitation of mass labels released from particles is also demonstrated.

Comparison of solvents for the recovery of low-molecular carboxylic acids and furfural from aqueous solutions

Liquid–liquid extraction of formic acid, acetic acid and furfural from an aqueous synthetic acid hydrolysis process stream is studied. Different types of extractants are first evaluated and two solvents that can efficiently recover the compounds, 2-methyltetrahydrofuran (2-MTHF) and tri-n-octylamine in toluene (Alamine 336-toluene) are then studied further. Important considerations in solvent selection were the efficiency of solvent regeneration and the recovery of the extractives from the loaded solvents. Solvent regeneration experiments were carried out under a vacuum in a spinning band distillation unit. Both solvents showed good regeneration characteristics. The rate of phase separation for Alamine 336 increased, without the formation of an emulsion, when performing extractions at low mixing rates. The use of toluene as a diluent for Alamine 336 prevented the formation of a third intermediate phase. In general, the equilibrium favors the extraction of formic acid for Alamine 336 and the extraction of furfural for 2-MTHF. For acetic acid there was only a small difference in the distribution coefficients for both solvents.

Sol–gel nanoporous silica as substrate for immobilization of conjugated biomolecules for application as fluorescence resonance energy transfer (FRET) based biosensor

Nanoporous silica beads with a particle size in the nanometer range, synthesized by adopting the sol–gel method, can be used as a dip-test platform for Förster Resonance Energy Transfer (FRET)-based sensing of troponin I, a regulatory protein for the contraction of cardiac muscles. The silica nanogel was synthesized using the sol–gel method, with tetraethoxysilane as the precursor, which was then subjected to hydrolysis in aqueous oxalic acid. The gel was molded and dried at 70°C, and subsequently calcined at 400°C. The silica substrate was then converted into a biosensor for troponin I by first silanizing, and then crosslinking Cy3 (FRET donor) labeled troponin I antibody (IgG) to which Cy5 (FRET acceptor) labeled Protein A was anchored. The potential of this biosensor to detect troponin I was examined using a combination of steady state fluorescence spectroscopy and microscopy. We found a considerable increase in the Cy3-to-Cy5 FRET efficiency as soon as troponin I was added to the biosensor. Results of this research show that the detection limit of troponin I using the FRET system is 10–5ngmL−1.

Production of hemicellulosic sugars from Pinus pinaster wood by sequential steps of aqueous extraction and acid hydrolysis

Pinus pinaster wood samples were subjected to aqueous extraction at 130°C to remove extractives and to a sequential stage of hydrothermal processing under selected operational conditions to obtain hemicelluloses-free solids and liquors containing hemicelluloses-derived products (mainly oligomeric saccharides and monosaccharides). Liquors were separated from the media, supplemented with sulfuric acid (4%), and heated to cause the posthydrolysis of oligomeric saccharides to yield hemicellulosic sugars. The effects of the major operational conditions on the yields of the target products were assessed in selected experiments. The considered process enabled the recovery of hemicellulosic sugars (mannose, glucose, xylose, and galactose) at almost quantitative yields.

ChemInform Abstract: Unexpected Hydrolysis of 5-Aminoisoxazolbenzoylamide Herbicide Isoxaben into 5-Isoxazolinone.

The benzoylamide derivative of 5-aminoisoxazol, i.e. the herbicide isoxaben 1 (N-[3-(1-ethyl-1-methylpropyl)isoxazol-5-yl]-2,6-dimethoxybenzamide) was transformed by aqueous acid hydrolysis into the unexpected 5-isoxazolinone 3 (3-(1-ethyl-1-methylpropyl)isoxazolin-5-one) plus mainly 2,6-dimethoxybenzamide 4. The expected 5-aminoisoxazol 7 (5-amino-3-(1--ethyl-1-methylpropyl)isoxazol) was not generated, except in very low amounts when high acid concentrations were used. In separate hydrolysis trials made in similar aqueous acid conditions, it was observed that the 5-aminoisoxazol 7 and 5-isoxazolinone 3 were not transformed. The 5-isoxazolinone 3 formed by isoxaben 1 acid hydrolysis thus was the first generated product, and was not formed by the consecutive nucleophilic substitution of 5-amino-isoxazol 7 which would have been formed in a first step. This unexpected 5-amino C-N bond cleavage by nucleophilic attack of H2O at the 5-C of the isoxazol ring of isoxaben 1 -instead of the usual amide CO-N bond cleavage- probably is due to the positive charge existing at the 5-C atom of the isoxazol ring. The acid hydrolysis pathway observed for isoxaben 1 also is the main soil metabolism pathway. The absence of formation of an aromatic amino compound by chemical hydrolysis reduces the concern as to their potential tranformation into carcinogenic nitroso or azo compounds in soil. On the other hand, isoxaben 1 was not hydrolyzed in aqueous dilute alkali.

ChemInform Abstract: 2′,3′-Anhydrouridine. A Useful Synthetic Intermediate.

2,2′-Anhydro-1-(β-D-arabinofuranosyl)uracil 1 reacts with sodium hydride in dry DMSO to give 2′,3′-anhydrouridine 2. When the latter compound 2 is heated below its melting point or treated with triethylamine in methanol, it isomerises back to the 2,2′-anhydronucleoside 1. Treatment of compound 1 with sodium ethanethiolate or the sodium salt of benzyl mercaptan in the presence of an excess of the corresponding thiol in DMA gives 2′-S-ethyl- or 2′-S-benzyl-2′-thiouridine (4 or 11) in high yield; however, treatment of the 2,2′-anhydronucleoside 1 first with sodium hydride in DMA and then with a deficiency (with respect to sodium hydride) of ethanethiol or benzyl mercaptan gives the corresponding 3′-S-ethyl or 3′-S-benzyl derivative (3 or 12) in high yield. When the 2,2′-anhydronucleoside 1 is allowed to react with an excess of potassium tert-butoxide in DMSO, the 3′,5′-anhydronucleoside 13 is obtained in good yield. The latter compound 13 undergoes hydrolysis in aqueous trifluoroacetic acid to give 1-(β-D-xylofuranosyl)uracil 14 in high yield. The 3′-S-benzyl derivative 12 is converted by Raney nickel desulfurisation into 3′-deoxyuridine 15 which, in turn, is converted into 3′-deoxycytidine 17 in good yield. X-Ray crystallographic data relating to compounds 11 and 12 are also reported.

Generation of Group B Soyasaponins I and III by Hydrolysis

Soyasaponins are a group of oleanane triterpenoids found in soy and other legumes that have been associated with some of the benefits achieved by consuming plant-based diets. However, these groups of compounds are diverse and structurally complicated to chemically characterize, separate from the isoflavones, and isolate in sufficient quantities for bioactive testing. Therefore, the aim of this study was to maximize the extraction of soyasaponins from soy flour, remove isoflavones, separate group B soyasaponins from group A, and produce an extract that contained a majority of non-DDMP (2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one)-conjugated group B soyasaponins I and III. Room temperature extraction in methanol for 24 or 48 h resulted in the maximum recovery of soyasaponins, and Soxhlet extraction resulted in the least. A solid-phase extraction using methanol (45%) was found to virtually eliminate the interfering isoflavones as compared to butanol-water liquid-liquid extraction and ammonium sulfate precipitation, while maximizing saponin recovery. Alkaline hydrolysis in anhydrous methanol produced the maximum amount of soyasaponins I and III as compared to aqueous methanol and acid hydrolysis in both aqueous and anhydrous methanol. The soyasaponin I amount was increased by 175%, and soyasaponin III was increased by 211% after alkaline hydrolysis. Furthermore, after alkaline hydrolysis, a majority of DDMP-conjugated group B soyasaponins such as betag, betaa, gammag, and gammaa transformed into the non-DDMP-conjugated soyasaponins I and III without affecting the glycosidic bond at position C-3 of the ring structure. Therefore, we have developed a method that maximizes the recovery of DDMP-conjugated saponins and uses alkaline hydrolysis to produce an extract containing mainly soyasaponins I and III.

Structure of a glycoglucuronomannan from the low-viscosity gum of Vochysia lehmannii

The polysaccharide (VSP) from the gum exudate of quaruba ( Vochysia lehmannii) had two components of almost identical M w centred at 24,800, as shown by HSPEC-MALLS. The presence of aggregates was shown since carboxy-reduction gave VSP-RED, which contained low molecular weight components with M w 19,000>5800 and polydispersity ratios d n/d c 0.160 and 0.149, respectively. VSP formed low viscosity aqueous solutions and acid hydrolysis gave Man (30%), Ara (16%), Gal (10%), and Glc (14%). The latter arose partly from GlcA (30%). Methylation analysis revealed mainly neutral units of 2- O- (60%) and 2,3-di- O-substituted Man p (5%), and those of nonreducing ends (8%), 2- O- (3%),and 4- O-substituted Ara p and/or 5- O-substituted Ara f units (6%). VSP-RED contained Glc (45%), Man (35%), and Ara (13%) and methylation analysis indicated mainly 4- O-substituted Glc p (31%) and 2- O- (51%) and 2,3-di- O-substituted Man p units (5%). A predominant alternating structure for VSP was shown by its 13C NMR spectrum, which contained 10 main signals and a small one of C-6 of Glc pA. This was confirmed by formation, on partial hydrolysis of VSP, of a tetrasaccharide, which was characterised by NMR spectroscopy and ESI-MS as β-Glc pA-(1→2)-α-Man p-(1→4)-β-Glc pA-(1→2)-Man, which arose from the main chain, thus confirming VSP to be a glycoglucuronomannan.

2′,3′-Anhydrouridine. A useful synthetic intermediate

2,2′-Anhydro-1-(β-D-arabinofuranosyl)uracil 1 reacts with sodium hydride in dry DMSO to give 2′,3′-anhydrouridine 2. When the latter compound 2 is heated below its melting point or treated with triethylamine in methanol, it isomerises back to the 2,2′-anhydronucleoside 1. Treatment of compound 1 with sodium ethanethiolate or the sodium salt of benzyl mercaptan in the presence of an excess of the corresponding thiol in DMA gives 2′-S-ethyl- or 2′-S-benzyl-2′-thiouridine (4 or 11) in high yield; however, treatment of the 2,2′-anhydronucleoside 1 first with sodium hydride in DMA and then with a deficiency (with respect to sodium hydride) of ethanethiol or benzyl mercaptan gives the corresponding 3′-S-ethyl or 3′-S-benzyl derivative (3 or 12) in high yield. When the 2,2′-anhydronucleoside 1 is allowed to react with an excess of potassium tert-butoxide in DMSO, the 3′,5′-anhydronucleoside 13 is obtained in good yield. The latter compound 13 undergoes hydrolysis in aqueous trifluoroacetic acid to give 1-(β-D-xylofuranosyl)uracil 14 in high yield. The 3′-S-benzyl derivative 12 is converted by Raney nickel desulfurisation into 3′-deoxyuridine 15 which, in turn, is converted into 3′-deoxycytidine 17 in good yield. X-Ray crystallographic data relating to compounds 11 and 12 are also reported.

Sterically Congested Molecules, 16 A Convenient Synthesis of Di‐tert‐butyl Ketone via its Imine, 2,2,4,4‐tetramethyl‐3‐pentanimine

Abstract2,2,4,4‐Tetramethyl‐3‐pentanimine (3) is efficiently prepared by a Barbier‐type reaction of pivalonitrile (1) with an excess of tert‐butyl chloride (2) and metallic lithium in ether. Its purification by extraction into aqueous acid and slow hydrolysis permit an inexpensive and very simple production of di‐tert‐butyl ketone (4).

Synthesis of aryl 3‐(2‐imidazolyl)propyl ketones

AbstractThe approach to the title compounds was via lithiation‐substitution of N‐methyl or N‐(triphenylmethyl)‐imidazole by some iodo ketals. 4‐Chloro‐4′‐halobutyrophenones (halo = F, Cl, Br) were converted by sodium iodide to the corresponding aliphatic iodides which were subsequently ketalized with ethylene glycol to provide the corresponding iodo ketals. Lithiation of either 1‐methyl‐ or 1‐(triphenylmethyl)imid‐azole with N‐butyllithium generated the corresponding 2‐lithioimidazoles, in situ, which were then reacted with these iodo ketals to form the corresponding C‐2 substituted imidazoles. Dilute aqueous acid hydrolysis released the ketone from the ketal. For N‐triphenylmethyl protected imidazoles, the triphenylmethyl group was also hydrolyzed to give triphenylmethanol and 3‐(2‐imidazolyl)propyl 4‐haloaryl ketones. These N‐unsubstituted imidazolyl ketones can be alkylated independently with triphenylmethyl chloride to form the corresponding N‐triphenylmethyl imidazole derivatives.

Physicochemical properties of mixed anionic–non-ionic micelles: effects on chemical reactivity

Addition of the non-ionic surfactant C16E20(C16H33[OCH2CH2]20–OH) to an aqueous acid solution of alkyl nitrites decreases its rate of acid hydrolysis. Kinetic data are analysed by using the pseudophase model, the partitioning of the alkyl nitrites between water and C16E20 micelles being the main reason for the observed inhibiton. The kinetic results provide for a quantitative estimate of the association constants.The observed rate constant of aqueous acid hydrolysis of alkyl nitrites increases in the presence of sodium dodecyl sulfate (SDS) micelles: first-order rate constants increase with increasing [SDS], go through maxima, and decrease at still higher concentrations of SDS. Addition of C16E20 to an aqueous acid solution of SDS strongly decreases the maximum for the observed rate constant, until at high [C16E20] : [SDS] ratio the observed rate constant decreases monotonically as the total surfactant concentration increases. Kinetic data are analysed by using the simple pseudophase ion-exchange model under the assumption that formation of mixed micelles in the binary mixed surfactant system (C16E20 and SDS) would occur. The properties of mixed micelles seem to be very different from those of pure surfactants. Binding constants and rate constants for the reaction in the micellar pseudophase, obtained from the kinetic analysis, are reported. Conductivity measurements were also taken.