The reaction of isocyanates with bisulphite salts

Abstract

Aliphatic isocyanates react rapidly and quantitatively with aqueous bisulphite solutions to form stable water-soluble adducts which are salts of N-alkylcarbamyl sulphonio acids. Phenyl isocyanate gives lower yields of the corresponding adduct which is less stable in water. The rate of reaction of n-butyl isocyanate with bisulphite increases with increasing p H and is proportional to [OH-] over the pH range from 5 to 8. The rate of decomposition of the butyl isocyanatebisulphite adduct increases with increasing temperature and pH. A plot of the logarithm of the initial first-order rate constant for the decomposition of the adduct against pH is linear over the pH range from 2 to 7 and has a slope of 0.57&0.05. Water-insoluble polymers with aliphatic isocyanate groups do not form bisulphite adducts under the conditions which are suitable for simple isocyanates. However, the addition of water-soluble organic solvents such as dioxan and the lower alcohols enables the preparation of water-soluble bisulphite adducts which are indefinitely stable a t room temperature and low pH. The relative quantity of the organic solvent must be kept within specific limits which depend on the nature of the prepolymer, the solids content of the final product, and the nature of the organic cosolvent.Polymers with isocyanate groups are used extensively to produce polyurethane coatings, elastomers, adhesives, and foams.la This use of polyisocyanates results from the ease with which condensation polymers form from the reactions of the isocyanates with nucleophiles (e.g. with alcohols to give polyurethanes). Hence isocyanates react readily with water (Scheme 1). This reaction with water can be RNCO + H 2 0 -RSHC02H -RSH2 + C02 RNHz + RSCO -RNHCONHR Scheme 1

Synthesis, characterization and thermal dissociation of 2‐butoxyethanol‐blocked diisocyanates and their use in the synthesis of isocyanate‐terminated prepolymers

“…Conjugation with aromatic nucli makes aromatic isocyanates particularly reactive, especially if electron‐withdrawing ring substituents are present, and even more so when they are present in the ortho or para position to the NCO group. Conversely electron‐releasing substituents depress the reactivity 48–50. It was observed that the gelation times of the isocyanate‐terminated prepolymers was in the order IPDI–HTPB prepolymer > HDI–HTPB prepolymer > TDI–HTPB prepolymer > MDI–HTPB prepolymer.…”

Polyurethanes

“…(23) Other types of curing systems for allyl-terminated urethane polymers were described by Kehr and Wszolek.68 Polyether and polyester urethane-ene systems were prepared by reaction of polyester or polyether .diols with allyl isocyanate or by reaction of polyester or polyether diols with allyl isocyanate or by reaction of isocyanate-terminated prepolymerswith 'allyl alcohol. Johnson and Labana"?…”

Easy One‐Pot Synthesis of a Reactive Hydrogel from Commercially Available 2‐Isocyanatoethyl Methacrylate and K2S2O5

“…In the less known hydrophilic series, bisulfites have been used to generate anionically charged sulfonato systems of general formula R-NH-C( --O) -SO À 3 . [2,6] Bisulfite salts are very efficient nucleophiles, known to react reversibly with aldehydes or ketones. The analogous reaction with isocyanates leads to the formation of water-soluble salts that can react with primary amines at or near C spectra of potassium n-butyl carbamoylsulfonate were recorded on a Bruker Avance II 400 NMR spectrometer.…”