Sk. Asrof Ali

The isoxazolidines: a new class of corrosion inhibitors of mild steel in acidic medium

Abstract The cycloaddition of the cyclic nitrone-1-pyrroline-1-oxide with a variety of alkenes, phenyl isocyanate and phenyl isothiocyanate afforded a multitude of cycloaddition products (isoxazolidines). One of the cycloadducts on reaction with benzyl and propargyl chloride gave quaternary ammonium salts. All these new isoxazolidines are tested for corrosion inhibition of mild steel in 1 M HCl at 60 °C by gravimetric and electrochemical methods. The inhibition efficiency of this class of compounds are determined for the first time. All compounds have shown excellent corrosion inhibition efficiency (IE%) in acidic solution; IE% in the range 86.7–99.5 are measured by the gravimetric method. Comparable results were obtained by the electrochemical method using Tafel plots for the inhibition efficiency of some of the selected synthesized compounds.

The regiochemistry and stereochemistry of 1,3-dipolar cycloaddition of cyclic nitrones

Abstract A comparative study of the regio- and stereo-chemical behaviour of the 1,3-dipolar cycloaddition of a series of alkenes with 1-pyrroline 1-oxide and 2,3,4,5-tetrahydropyridine 1-oxide has been carried out. The high degree of both regio- and stereochemical control observed in these reactions has been explained in terms of frontier orbital interaction, steric factors, and secondary orbital interaction in the transition state. While most common alkenes (both mono- and 1,1-di-substituted) gave 2-substituted cycloadducts, highly polarized alkene dimethyl methylenemalonate afforded mainly regioisomeric 3-substituted cycloadduct. Significant secondary orbital interaction is observed with the non-conjugated substituents, hydroxymethyl and its derivatives.

Protein partitioning in aqueous two-phase systems composed of a pH-responsive copolymer and poly(ethylene glycol).

The effect of pH and salt concentration on the partitioning behavior of bovine serum albumin (BSA) and cytochrome c in an aqueous two‐phase polymer system containing a novel pH‐responsive copolymer that mimics the structure of proteins and poly(ethylene glycol) (PEG) was investigated. The two‐phase system has low viscosity. Depending on pH and salt concentration, the cytochrome c was found to preferentially partition into the pH‐responsive copolymer‐rich (bottom) phase under all conditions of pH and salt concentrations considered in the study. This was caused by the attraction between the positively charged protein and negatively charged copolymer. BSA partitioning showed a more complex behavior and partitioned either to the PEG phase or copolymer phase depending on the pH and ionic strength. Extremely high partitioning levels (partition coefficient of 0.004) and very high separation ratios of the two proteins (up to 48) were recorded in the new systems. This was attributed to strong electrostatic interactions between the proteins and the charged copolymer.

Reactivity, regiochemistry, and stereochemistry of a cyclic nitrone and its α-keto derivative in 1, 3-dipolar cycloaddition reactions

Abstract Rate constants for the cycloadditions of 3,4,5,6-tetrahydropyridine 1-oxide ( 1 ) , and 3-oxo-3,4,5,6-tetrahydropyridine 1-oxide ( 2 ) to several mono- and disubstituted alkenes have been determined at 36°C by 1H NMR Spectroscopy. Small solvent effect on the rate constant indicate the concerted nature of the reaction. It is found that nitrone 2 reacts slower than 1 because of the presence of bond opposition strain in the transition state for the former nitrone. Addition rates are influenced by the dipole moments of the nitrones. Reactivity of these addition reactions usually follows the prediction of frontier orbital approximation. Both the nitrones exhibit very similar regiochemical and stereochemical properties. Significant secondary orbital interaction is observed with several electron deficient alkenes. However, maleic anhydride is found to undergo addition predominantly via exo mode of attack.

Synthesis and solution properties of a new pH-responsive polymer containing amino acid residues

Abstract The amine salt, N,N-diallyl-N-carboethoxymethylammonium chloride was cyclopolymerized in water using ammonium persulfate as an initiator to afford a cationic polyelectrolyte which on acidic hydrolysis of the pendant ester groups gave the corresponding cationic acid salt (CAS). The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB). The solution properties of the APE having two basic functionalities were investigated in detail by potentiometric and viscometric techniques. Basicity constants of the amine as well as the carboxylate groups in APE are ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; as the degree of protonation (α) of the whole macromolecule increases, the protonation of the amine nitrogens and carboxylate groups becomes increasingly more difficult and easier, respectively. While the APE, PB and CAS were found to be soluble in salt-free water, the corresponding PB and CAS of the SO2 copolymers of the amine salt 1 were found to be insoluble in water.

Synthesis and solution properties of a new ionic polymer and its behavior in aqueous two-phase polymer systems

Abstract The amine salt, N , N -diallyl- N -carboethoxymethylammonium chloride was copolymerized in dimethyl sulfoxide using ammonium persulfate or azo-bis-isobutyronitrile (AIBN) to afford the cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) having the equivalent of chloride salt of N , N -diallylammonio ethanoic acid as monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB) [having the monomeric unit equivalent of sodium N , N -diallylaminoethanoate and N , N -diallylammonioethanoate] by treatment with two and one equivalent of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. Basicity constant of the amine functionality in APE is found to be ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; the protonation of the APE becomes more and more difficult as the degree of protonation ( α ) of the whole macromolecule increases. The composition and phase diagram of the aqueous two-phase systems of APE and poly(ethyelene glycol) (PEG) has been studied for the first time for this class of ionic polymers. The CAS and PB were found to be virtually insoluble in water.

Synthesis and solution properties of a betaine-sulfur dioxide polyampholyte

Abstract The copolymer 7 of quaternary ammonium salt, N , N -diallyl- N -carboethoxymethyl- N -methylammonium chloride ( 5 ) and sulfur dioxide were synthesized in excellent yield. The polyelectrolyte 7 on acidic hydrolysis gave the polyampholyte 8 readily in excellent yield. The solution properties of these polymers are discussed in detail. The polyampholyte 8 was found to be insoluble in water but dissolved readily in the presence of low molecular weight common salts. The polyampholyte shows “anti-polyelectrolyte” behavior; the viscosity of the polyampholyte increases by increasing the ionic strength of its aqueous solutions.

Synthesis and aqueous phase behaviour of homo- and copolymers of 1,1-diallyl-4-formylpiperazinium chloride

The quaternary ammonium salt, 1,1-diallyl-4-formylpiperazinium chloride (3) on cyclopolymerization in water solution in the presence of t-butylhydroperoxide gave water soluble polymer (5). The copolymers of (3) with sulfur dioxide have been prepared in DMSO solvent using ammonium persulfate as the initiator. The composition and phase diagram of the aqueous two-phase systems of the homopolymer (5) and copolymer (8) has been studied for the first time for this class of polymers. Synthesis of the polymer (8) paves the way for the preparation of a new class of polymers with a basic trivalent nitrogen as well as a quaternary nitrogen.

Synthesis and solution properties of a quaternary ammonium polyelectrolyte and its corresponding polyampholyte

Abstract The quaternary ammonium salt, N,N-diallyl-N-5-carbomethoxypentyl-N-methylammonium chloride (DACPMAC), on cyclopolymerization in aqueous solution using tert-butylhydroperoxide, afforded the polyelectrolyte poly(DACPMAC), having five-membered cyclic structure on the polymeric backbone, in excellent yield. The polyelectrolyte on acidic hydrolysis of the pendent ester groups gave the corresponding polyampholyte poly(DAMAH) having the equivalent of 6-(N,N-diallyl-N-methyl ammonio) hexanoate (DAMAH) as monomeric unit. The solution properties of these polymers as well as the polyelectrolyte, poly(DACMMAC), and its corresponding polyampholyte, poly(DAMAE), [having the monomeric unit equivalent of N,N-diallyl-N-carboethoxymethyl-N-methylammonium chloride (DACMMAC) and N,N-diallyl-N-methyl ammonio ethanoate (DAMAE)] are investigated by potentiometric and viscometric techniques. Basicity constants of the polyampholytes are found to be ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation. While the protonation of the polyampholyte poly(DAMAH) becomes more and more difficult as the degree of protonation (α) of the whole macromolecule increases, the polyampholyte poly(DAMAE), exhibits the reverse trend i.e. the protonation process becomes easier and easier with increasing α.

Polymerization of functionalized diallyl quaternary ammonium salt to poly(ampholyte–electrolyte)

Abstract The quaternary ammonium salt, N,N-diallyl-N-carboethoxymethyl-N-carbomethoxypentylammonium chloride 13, on polymerization in aqueous solution using tert-butylhydroperoxide, afforded the polyelectrolyte 14. The copolymer 15 of the monomer 13 and sulfur dioxide was synthesized in excellent yield. The polyelectrolytes 14 and 15 on acidic hydrolysis gave the poly(ampholyte–electrolytes) 16 and 17 which contain structural features common to both polyampholytes and conventional polyelectrolytes. The solution properties of these polymers are discussed in detail. The poly(ampholyte–electrolyte)s, 16 and 17 are shown to have considerably higher viscosity than their corresponding polyelectrolytes 14 and 15.