Aqueous Mineral Acid Research Articles

Lactams in sulfuric acid. The mechanism of amide hydrolysis in weak to moderately strong aqueous mineral acid media

Reaction rate constants obtained in moderately concentrated sulfuric acid for the hydrolysis of simple lactams of ring sizes five, six, seven, and eight as a function of acidity and temperature have been analyzed using the excess acidity kinetic method. The basicity constants for these substrates have been recalculated; the 13C NMR spectra used to obtain these values are very sensitive to medium effects. It was found that the basicities of the lactams at 0.003-0.1 M lactam concentration were over half a pK unit more basic than they were at 0.5 M lactam, presumably because of the medium effect. Apart from this, the rate constant results obtained at different times by different groups using different techniques for monitoring the kinetics are in adequate agreement. The excess acidity analysis showed that the kinetics could be fitted according to the "three-water-molecule followed by one-water-molecule" mechanistic scenario previously found, or could just as well be fitted by a "one-water-molecule followed by unknown mechanism" scenario, with the mechanistic change taking place at 50 wt.% sulfuric acid for all the substrates. Other evidence makes the latter seem the more likely possibility of the two, and activation parameters based upon the "one-water-molecule" process were determined. Sufficient data points to enable the unknown mechanism to be established were not present; possible mechanisms applicable in media more concentrated than 50 wt.% sulfuric acid are discussed. Previously obtained values of the parameter r, the number of water molecules involved with the substrate in A2 processes, are now questionable.Key words: amides, lactams, excess acidity, hydrolysis, mechanism.

Synthesis and characterization of actinide-exchanged Preyssler heteropolyanions [AnP 5W 30O 110] n− (An≡Th, Am, Cm)

Interest in the use of heteropolyoxometalate clusters as actinide complexants motivates our studies of the Preyssler heteropolytungstate anion, [NaP 5W 30O 110] 14−, and its actinide-exchanged derivatives, [AnP 5W 30O 110] n− . Under specific conditions, substitution of Na + is possible by La 3+ and Th 4+ as well as by U 4+ and the transuranics Am 3+ and Cm 3+. Both [AnP 5W 30O 110] 11− (for An≡Th 4+, U 4+) and [AnP 5W 30O 110] 12− (for An≡Am 3+, Cm 3+) as well as [LaP 5W 30O 110] 12− exhibit remarkable redox properties and form heteropoly blues. Although similar, the electrochemistry of the An 3+/La 3+- and An 4+-exchanged anions are different and distinguishable by cyclic voltammetry in aqueous mineral acid electrolytes. The synthesis of the new Preyssler anion complexes of La 3+, Th 4+, Am 3+, and Cm 3+ will be described along with results from cyclic voltammetry measurements.

Lactams in sulfuric acid. The mechanism of amide hydrolysis in weak to moderately strong aqueous mineral acid media

Lactams in sulfuric acid. The mechanism of amide hydrolysis in weak to moderately strong aqueous mineral acid media

The mechanism of the hydrolysis of acylimidazoles in aqueous mineral acids. The excess acidity method for reactions that are not acid catalyzed

The mechanism of the hydrolysis of acetylimidazole in aqueous perchloric, sulfuric, and hydrochloric acid mixtures has been determined. Benzoylimidazole was also studied in the latter two acids. The method of analyzing the available data, pseudo-first-order reaction rate constants as a function of acid concentration and, in one case, temperature, is the excess acidity method, here applied to the same reaction in the three different acid media, allowing their comparison. The reaction is not acid catalyzed; the rates decrease with increasing acidity. The substrate reacts in the form that is monoprotonated on the imidazole ring; it is 100% protonated at acidities much lower than those used here. Acetylimidazole is shown to become diprotonated at high acidity [Formula: see text], protonating on the carbonyl oxygen, but the diprotonated form is not reactive. The hydrolysis involves the reversible addition of one water molecule to the substrate to give a tetrahedral intermediate; at low acidities the decomposition of this hydrate is the rate-determining step, but as the acidity increases and the water activity decreases its formation becomes rate limiting. Hydroxide catalysis was also observed in dilute perchloric acid, but this is swamped by nucleophilic catalysis by the acid anion in HCl and H2SO4. Keywords: acylimidazoles, excess acidity, hydrolysis, protonation, tetrahedral intermediate.

Removal of Alkaline Catalysts from Polyols by Ion Exchange

Abstract Resin regeneration is crucial in the feasibility of polyol purification by ion exchange. In order to get an economically viable commercial process, a new regeneration process, including initial and final methanol flushing steps and treating with a 4.5 M aqueous mineral acid solution, has been investigated. An important reduction in regeneration costs was reached by minimizing the amount of acid used and recycling one part of the regenerant solution to the process. The composition of regeneration effluents has been studied in order to recover their valuable components. This simple resin regeneration technique lends itself to a technically and economically viable commercial process for the treatment of polyol products.

Propane Solubility in Aqueous Mineral Acids (0–100%): a Significant Difference in the Solvating Properties of H 2SO 4, HNO 3 and H 3PO 4

Unexpectedly high differences in propane solubility in the systems HNO 3 –H 2 O (salting-in), H 3 PO 4 –H 2 O (salting-out) and H 2 SO 4 –H 2 O (salting-out at low H 2 SO 4 concentrations and salting-in at high concentrations) have been revealed, and the data quantitatively interpreted within the framework of the previously suggested equation relating the excess amounts of solubility with the molar volume of a system; the general nature of these equations for systems of this type has been demonstrated.

Selectivity in Stripping of Alkali-Metal Cations from Crown Ether Carboxylate Complexes

Abstract The potential of crown ethers (macrocyclic polyethers) as the next generation of specific extracting agents for metal ions was markedly enhanced by the introduction of crown ethers which bear pendent proton-ionizable groups (1–5). It has been shown that metal ion extraction does not require concomitant transfer of an aqueous phase anion into the organic medium (6). For potential practical applications of these proton-ionizable crown ethers in which hard aqueous phase anions (chloride, nitrate, sulfate) would be involved, this factor is of immense importance. In addition, the combination of ion binding cavities possessing fixed dimensions with protonionizable groups creates novel bifunctional chelating agents. A final factor is the case with which extracted metal ions may be stripped from the organic phase by shaking with aqueous mineral acid.

Tetrazolverbindungen. 4 [1]. Alkylierung von 1‐Aryl‐5‐(2‐dimethylamino‐vinyl)‐1 H‐tetrazolen

Tetrazole Compounds. 4. Alkylation of 1‐Aryl‐5‐(2‐dimethylamino‐vinyl)‐1 H‐tetrazolesAlkylation of 1‐aryl‐5‐(2‐dimethylamino‐vinyl)‐1 H‐tetrazoles 1 with dialkyl sulfates or alkyl iodides yields mainly 4‐alkyl‐1‐aryl‐5‐(2‐dimethylamino‐vinyl)‐1 H‐tetrazolium salts which can be isolated free from isomers by separation as perchlorates 2. The reaction proceeds with retention of the E configuration of the vinyl group. In contrast to 1 the methyl groups of the dimethylamino substituent in 2 are magnetically non‐equivalent indicating restricted rotation of this residue. On heating 2 with aqueous mineral acids the dimethylaminovinyl moiety undergoes degradation to a methyl group affording 4‐alkyl‐1‐aryl‐5‐methyl‐1 H‐tetrazolium salts 4, the structure of which was confirmed by independent synthesis. With hot aqueous alkali hydroxide 2 reacts under ring cleavage to give aryl azide. — 1H n.m.r. and u.v. spectroscopic data of the tetrazolium salts 2 and 4 are reported.

Liquid — Liquid extraction of silver(I) by diphenyl-2-pyridylmethane in benzene from aqueous mineral acid — Thiocyanate solutions

Liquid — liquid extraction of Ag(I) by diphenyl-2-pyridylmethane (DPPM) in benzene from aqueous nitric and sulfuric acid solutions containing thiocyanate ions has been studied at ambient temperature (24±2 °C). The metal is extracted quantitatively from 0.01M HNO3+0.02M KSCN; or 0.25M H2SO4+0.02M KSCN by 0.1M DPPM (optimum extraction conditions). Slope analysis indicates that two types of ion-pair complexes i.e. [(DPPMH)+·Ag(SCN) 2 − ] and [(DPPMH) 2 + ·Ag(SCN) 3 2− ] are involved in the extraction process. Separation factors determined at optimum conditions reveal the separation of Ag(I) from Cs(I), Br(I), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Fe(III), Au(III) (from HNO3 solution only), Cr(III), Hf(IV), Ta(V), Sn(IV) and Cr(VI). With the exception of thiosulfate, other complexing anions like ascorbate, acetate, citrate, oxalate do not hinder the extraction of Ag(I) under optimum conditions.

Intercalation reactions of ruthenium-(III)-chloride via electron/ion transfer

The layered anisotropic semiconductor α-RuCl 3 is able to undergo a wide variety of intercalation reactions via electron/ ion transfer and subsequent exchange reactions. The structures of hydrated phases (A n+ ) x/n (H 2O) y [RuCl 3] x- wit h alkali, alkaline earth and transition metal ions are related to the hydration enthalpies of the guest cations. The hydrated phases are polyelectrolytes and show cooperative ion exchange phenomena. Cathodic reduction of α-RuCl 3 in concentrated aqueous mineral acids yields the hydrogen bronze H x RuCl 3 while from dilute acids hydronium phases (H 3O +) x (H 2O) y [RuCl 3] x- are obtained whose hydrate structures are dependent upon the acid concentration. Among the cations which intercalate as unsolvated species (Cu +, Ag +, Tl +) the copper phases exhibit different reaction mechanisms in aqueous and aprotic electrolytes. A comparison of the topotactic reactivity of α-RuCl 3 and of layered transition metal dichalcogenides MX 2 reveals a remarkable similarity.

Pyrrolidine Carboxaldehyde Hydrohalide Catalyzed Halogenations of Aliphatic Aldehydes

Abstract Efficient methods for the direct chlorination or bromination of aliphatic aldehydes to their corresponding α,α-dihalo aldehydes in high yield and purity are unknown. Many approaches have suffered from one or more of the following, formation of byproducts, aldol condensations incomplete conversions and losses through tedious workup procedures. Early investigations have shown that the vapor phase chlorination of aliphatic ketones has produced good yields of 2-chloro ketones,(1) while the vapor phase chlorination of aliphatic aldehydes has resulted in the formation of acid chlorides.(2) One of the first successful acid catalyzed chlorinations of propionaldehyde was reported by Dick(3) who obtained 50–60% yields of 2,2-dichloropropionaldehyde accompanied by aldol condensations and polyhalogenated trioxanes. The reaction was carried out in standardized aqueous mineral acid solutions and the product was isolated by means of a laborious azeotropic distillation. The use of sulfuryl chloride in the presence of a catalytic amount of diphenyl sulfide for the chlorination of aldehydes was shown by Dalman(4) to give 60–70% yields of 2-chloro and 2,2-dichlorinated aldehydes. Clean separations i.e. products free of sulfuryl chloride could only be obtained by distillation with a spinning band column at high reflux ratios.

Extraction of molybdenum(VI) by 4-(5-nonyl)pyridine in benzene from aqueous mineral acid solutions containing thiocyanate ions

Extraction of Mo(VI) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiocyanate ions has been investigated at room temperature (23±2°C). From mineral acid (HCl, HNO3, and H2SO4) solutions alone Mo(VI) is not extracted quantitatively while the presence of small amounts of KSCN in the system augments the extraction by a large factor. Stoichiometric studies indicate that ion-pair type complexes (NPyH)2·[MoO2(SCN)4] are responsible for the extraction. Separation factors determined at fixed extraction conditions (0.1M Npy/C6H6−0.1M acid +0.2M KSCN) reveal that Ag(I), Cu(II), Co(II), Zn(II), Hg(II) and U(VI) are co-extracted while a clean separation from alkali metals, alkaline earths and some transition metals like Ln(III), Zr(IV), Hf(IV), Cr(III), Cr(VI) and Ir(III) is possible. Some of the complexing anions like oxalate, citrate, acetate, thiosulfate or ascorbate do not affect the degree of extraction of Mo(VI) allowing it to be recovered from diverse matrices.

Search for optimal conditions for the extraction of thiosulfate complexes of Cu(II) by 4-(5-nonyl)pyridine from aqueous mineral acid solutions

Solvent extraction of Cu(II) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiosulfate ions has been studied at room temperature (23±2°C). Mineral acid solutions alone constitute an aqueous phase from which Cu(II) is not extracted. Addition of small amounts of thiosulfate ions augments the extraction to an extent that quantitative recovery is possible. Stoichiometric studies reveal the involvement of ion-pair type complexes (NPy·H)2·Cu(S2O3)2 which are responsible for extraction. Stability constants lg Kex for this complex are 7.2±0.2; 9.1±0.2 and 9.5±0.2 for HCl, HNO3 and H2SO4, respectively. The presence of 0.01 mol/l of some complexing ions like ascorbate, acetate, citrate, oxalate, tartrate or iodide does not affect the extraction, thus allowing the recovery of the metal from diverse matrices. Under optimal conditions (0.1M NPy in benzene-0.1M HNO3 or H2SO4+0.01M S2O3−2 or 0.5M HCl+0.05 M S2O3−2) a clean separation from some elements, e.g. Cs(I). Co(II), Fe(III), Eu(III), Ce(III), Se(IV) and Cr(VI) can be achieved.

Solvent extraction of zinc by 2-hexylpyridine in benzene from aqueous mineral acid — Thiocyanate media

Solvent extraction of Zn(II) by 2-hexylpyridine (HPy) in benzene has been studied from aqueous mineral acid—thiocyanate media. The extraction, though dependent on the acidity of the aqueous phase, is poor from mineral acids (HCl, HNO3 or H2SO4). Addition of 0.02M KSCN to the aqueous phase enhances the distribution ratio by a factor of almost one thousand. The stoichiometry of the extracted complex established by the usual slope analysis method indicates that an ionic type complex, e.g. Zn(SCN)4·(HPyH)2, is responsible for extraction. Complexing anions like acetate, oxalate or citrate at 1 M concentration mask the extraction of Zn(II) almost completely. Separation factors determined at optimal conditions (0.1M HPy in benzene −0.05M H2SO4+0.2M SCN−) indicate that Zn(II), along with Hg(II), can be separated in a single extraction from a number of metals, e.g. Cs(I), Sr(II), Ln(III), Y(III), Cr(III) and (VI). Other metals of interest like Cu(II), Co(II), Fe(III), Mo(VI), U(VI) and Tc(VII) are coextracted but the separation factors are large enough to allow separation in a multistage extraction process.

Syntheses of 2-Alkyl-2-cyclopentenones and 2-Alkylcyclopentanones from 1-Alkyl-cis-2, 3-epoxycyclopentanols

A mixture of 2-alkyl-2-cyclopentenone (2) and 2-alkylidenecyclopentanone (3) was obtained in good yield by the treatment of 1-alkyl-cis-2, 3-epoxycyclopentanols (1) in an aqueous mineral acid. In case of the use of aqueous 10% hydrochloric acid, 1-alkyl-3-chloro-1, 2-cyclopentanediols (4) were produced remarkably. It was presumed that (2) and (3) were produced via the enol forms by intramolecular dehydrochlorination of (4).cis-1, 2-Diols (5) were produced nearly quantitatively by the reduction of (1) with LiAlH4 in dried tetrahydrofuran. When (5) were reacted in an aqueous mineral acid, 2-alkylcyclopentanones (6) were obtained in 8895% yield. It was suggested that (6) were produced via the enol form by dehydration of (5).

The acid-catalysed hydrolysis of episulphoxides

The acid-catalysed hydrolyses of a number of episulphoxides in aqueous mineral acids have been studied. Ethylene, propylene, and styrene episulphoxides hydrolyse by concurrent A-2 and nucleophile-catalysed pathways. 3-Methyl- and 3,3-dimethyl-butylene 1,2-episulphoxide hydrolyse in sulphuric acid by an A-2 mechanism but in concentrated perchloric acid their rate profiles pass through a maximum and there is a changeover from an A-2 to an A-1 mechanism. Values of pKBH+ for these two episulphoxides have been determined.

Extraction of UO 22+ by two hindered (GO) (ClCH 2)PO(OH) extractants, in benzene and n-heptane diluents, from aqueous chloride and nitrate phases

The extraction of U(VI) from an aqueous mineral acid phase by a hindered (GO)(ClCH 2)PO(OH) extractant in a carrier diluent was studied as a function of the hydrogen ion concentration in the aqueous phase, steric hindrance within the extractant molecule, nature of the carrier diluent and composition of the aqueous phase. The two extractants were 2,6-iso-propyl phenyl chloromethyl phosphonic acid, [2,6-( i-C 3H 7) 2C 6H 3O] (ClCH 2)PO(OH), symbolized as H(2,6-Pφ)[( CIM) P] and 2,6-sec-butyl phenyl chloromethyl phosphonic acid, [2,6-( s-C 4H 9) 2C 6H 3O] (ClCH 2)PO(OH), symbolized as H(2,6-sBφ)[( ClM) P]. The carrier diluents were benzene and n-heptane. The aqueous phases were 1.00 F(HCl + NaCl) and 1.00 F(HNO 3 + NaNO 3). The extractant and hydrogen ion dependencies were found to be 2.0-power, respectively. Comparison of extraction of U(VI) in terms of the various parameters show the following ratios of K s values: H(2,6- iPφ) [(ClM)P]/H(2,6-sBφ)[(ClM)P], 2.5; in n-heptane/in benzene, 10; and from NO 3 −/from Cl −, 1.5. The K s is defined by the expression K= K sF 2 [H] +] 2 where K is the distribution ratio, F is the concentration of extractant in the organic phase, [H +] is the concentration of H + in the aqueous phase and K s is a constant characteristic of the system.

Vinyl ether hydrolysis. XV. Methyl β,β-di-tert-butylvinyl ether: buttressing steric effects

The highly congested molecule, methyl β,β-di-tert-butyl vinyl ether, undergoes reaction in dilute aqueous mineral acid solutions by a normal vinyl ether hydrolysis mechanism and gives an unrearranged aldehyde product. The tert-butyl groups retard the rate of hydrolysis, but the effect of cis and trans substituents is not cumulative; this is attributed to a repulsive nonbonded interaction, relieved in the course of reaction, between the ether oxygen atom and the cis-tert-butyl group buttressed by the trans-tert-butyl group.

Activation of ZSM-5 catalysts

Greatly increased yields of aromatics were obtainied in the reaction of ethanol over ZSM-5 zeolites if the protonated catalyst was pretreated in aqueous mineral acids or if hydrogen choloride or dichloroethane was added to the feed. The treated catalysts apparently contained less sodium than the ammonium-exchanged catalysts, and in some cases, some alumimum was removed. The product distributions at > 95% conversion were, e.g., 2% by wt benzene, 12% toluene, 24% xylenes, 34% trimethylbenzene, and 11% C/sub 10/+ aromatics from a catalyst treated in 0.6 M nitric acid, and 3% xylenes and 92% C/sub 10/+ aromatics from a catalyst treated in hydrofluoric acid.

Extraction of some elements of the groups IV b and VI b with 1-phenyl-3-methyl-4-caproyl-pyrazolone-5 (PMCP) from aqueous mineral acid solutions

Solvent extraction of Cr(VI), Mo(VI), W(VI) and Hf(IV) with 1-phenyl-3-methyl-4-caproyl-pyrazolone-5 (PMCP) in methyl isobutylketone (MIBK), xylene and chloroform (CHCl3) from mineral acid solutions was studied. Chromium(VI) is not extracted from any of the acids studied (HCl, H2SO4 and HClO4). Molybdenum(VI) is quantitatively extracted by the reagent in xylene and CHCl3 from HClO4 and HNO3 solutions. It is also extracted quantitatively by the reagent in MIBK from HCl, HNO3 and H2SO4 solutions but the participation of the diluent as extractant is considerable. Tungsten(VI) is quantitatively extracted in xylene from 9M HClO4 solution. MIBK used as diluent also affects its extraction with PMCP. Hafnium(IV) is not extracted from H2SO4 solutions while it extracts more than 99% at 3M HNO3 and above. The extracted species likely are: MoO2(PMCP)2, WO2(PMCP)2 and Hf(PMCP)4, respectively.