A method for accelerating a reaction of an organic compound containing a reactive -NCY radical in which Y is oxygen or sulphur with a compound containing a reactive hydrogen atom or atoms comprises conducting the reaction in the presence of an organic compound having at least one direct bond between a carbon atom and an atom (referred to as a "key atom") of an element in Group V(B) and having an atomic weight of over 74 (i.e. arsenic, antimony or bismuth). The method is applicable in the production of foamed and homogeneous polyurethanes. The organic compound may, in addition, have one or more bonds from a key atom to a halogen, hydrogen, oxygen, sulphur, nitrogen or phosphorus atom. Types of compound referred to are (a) compounds having 3 or 5 carbon to key atom bonds, such as tributylarsine, pentaphenylantimony; (b) compounds having one carbon to key atom bond in which the remaining valences of the key atom are taken up by hydrogen or halogen atoms or hydroxyl groups, such as octyl arsine, phenylarsine sesquisulphide, triphenyl stibine iodide cyanide, and tetrabutylarsonium hydroxide; (c) compounds having up to three direct bonds between carbon and key atoms and at least one double bond from the key atom to oxygen or sulphur, such as tributylarsine sulphide; (d) compounds having in addition to the carbon to key atom link both a double bond to oxygen or sulphur and a bond from the key atom to a halogen atom or hydroxyl group, such as phenyl dichloroarsine oxide; (e) compounds having in addition to the key atom to carbon bond the remaining valences occupied by bonds to oxygen, sulphur, nitrogen or phosphorus linking organic radicals to the key atom, such as butyldioctoxyarsine; (f) compounds having two or more key atoms which may or may not be bonded together and have in addition to the key atom to carbon bond also bonds to hydrogen, halogen, oxygen, sulphur, nitrogen or phosphorus such as bis-(dibutylarsenic) oxide. Many more specific compounds in each class are given. In examples, foams are prepared by reacting an adipic acid/1,2,6-hexanetriol polyester, toluene-2,4- and 2,6-diisocyanates and water in the presence of an emulsifying agent and (a) tri-n-butyl-stibine oxide; (b) tri-n-butylarsine oxide; (c) (for comparison) N-methylmorpholine. In alternative polyisocyanates of the formula R(NCY)x where x is two or more, R can be hydrocarbon or of the type-R-Z-R-where Z is, for example, -O-,-OR-O, -CO-,-CO2-, -S-, -S-R-S, or SO2. Examples include 1,8-diisocyanato-p-menthane, xylylene diisocyanates, (OCNCH2CH2CH2OCH2)2, xylylene-a ,a 1-diisothiocyanate and isopropylbenzene-alpha-4-diisocyanate, polymeric diisocyanates and compounds of the formula M(NCY)x in which x is a monofunctional atom or group, such as ethyl-phosphonic diisocyanate, phenyl-phosphonous diisocyanate, compounds containing a Si-NCY group, and isocyanates derived from sulphonamides. As compounds containing active hydrogen there can be used glycols, glycerol, 1,2,6-hexane-triol, sorbitol, dextrin, starch, cellulose, polyvinyl alcohol, ethylene-vinyl alcohol copolymers, cellulose acetate, shellac, castor oil, polyesters, alkyd resins, polyvinyl acetals or ketals, polyethers, polyetheresters, polyacrylic acids, ethylene diamine, hexamethylene diamine, ethanol-amines, polyesteramides, poly(hexamethylene adipamide), wool and proteins, and glass and metals which have a thin layer of water on their surface.ALSO:A method for accelerating a reaction of an organic compound containing a reactive-NCY radical in which Y is oxygen or sulphur with a compound containing are active hydrogen atom or atoms comprises conducting the reaction in the presence of an organic compound having at least one direct bond between a carbon atom and an atom (referred to as a "key atom") of an element in Group V (b) and having an atomic weight of over 74 (i.e. arsenic, antimony or bismuth). The organic compound may, in addition, have one or more bonds from a key atom to a halogen, hydrogen, oxygen, sulphur, nitrogen or phosphorus atom. Types of such compound referred to are (A) compounds having 3 or 5 carbon to key atom bonds, such as tributylarsine or pentaphenylantimony; (B) compounds having one key atom to carbon bond in which the remaining valences of the key atom are taken up by hydrogen or halogen atoms or hydroxyl groups, such as octyl arsine, phenylarsine sesquisulphide, triphenyl-iodide cyanide, and tetrabutylarsonium oxide; (C) compounds having up to three single carbon to key atom bonds and at least one double bond from the key atom to oxygen or sulphur, such as tributylarsine sulphide, (D) compounds having in addition to the carbon to key atom link both a double bond to oxygen or sulphur and bond from the key atom to halogen or hydroxyl, such as phenyl-dichloroarsine oxide; (E) compounds having in addition to the carbon to key atom link the remaining valences occupied by bonds to oxygen, sulphur, nitrogen or phosphorus, linking organic radicals to the key atom, such as butyl dioctoxyarsine; (F) compounds having two or more key atoms which may or may not be bonded together and have in addition to the key atom to carbon bond also bonds to hydrogen, halogen, oxygen, sulphur, nitrogen or phosphorus, such as bis (dibutylarsenic) oxide. Many more specific compounds in each p class are given. A table shows the effect on the rate of reaction of phenyl isocyanate and methanol of phenyl dichlorostibine and of trisubstituted arsine, stibine and bismuthine and the corresponding oxides, in which the substituents are selected from ethyl, n-butyl, n-octyl and phenyl groups, in comparison with p-toluenesulphonic acid, acetic acid, N-methylmorpholine, triethylamine, triphenylamine, cobalt naphthenate, sodium methoxide and ferric chloride catalysts. Other reactants specified, in addition to those giving polymers (see Group IV(a)) include compounds of the formula RNCY in which R is an alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, aryl or alkaryl radical which may be substituted, and also a number of polyfunctional isocyanates and isothiocyanates including, besides the more usual types, ethylphosphonic diisocyanate, phenylphosphonous diisocyanate, isocyanates from sulphonamides, cyanic acid, thiocyanic acid and tributyltin isocyanate. Active hydrogen-containing compounds specified are water, hydrogen peroxide, alcohols, hydroperoxides, phenols, boronic acids, carboxylic acids, percarboxylic acids, sulphonic acids, ammonia, amines, amides, lactams, ureas, urethanes, allophanates, biurets, acyl ureas, thioureas, hydrazines, oximes, amidines, hydroxylamines, hydrazones, hydroxamic acids, nitramines, diazoamine compounds, sulphonamides, mercaptans, thiophenols, thioacids, halogen acids, acetone, malonic esters, acetoacetic esters, acetylacetone, nitromethane, acetylenic compounds and dialkyl phosphonates, as well as the compounds containing two or more active hydrogen-containing groups, (see Group IV(a)).ALSO:A method for accelerating a reaction of an organic compound containing a reactive -NCY radical in which Y is oxygen or sulphur with a compound containing a reactive hydrogen atom or atoms comprises conducting the reaction in the presence of an organic compound having at least one direct bond between a carbon atom and an atom (referred to as a "key atom") of an element in Group V(B) and having an atomic weight of over 74 (i.e. arsenic, antimony or bismuth). The method is applicable in the production of foamed and homogeneous polyurethanes. The organic compound may, in addition, have one or more bonds from a key atom to a halogen, hydrogen, oxygen, sulphur, nitrogen or phosphorus atom. Types of compound referred to are (A) compounds having 3 or 5 carbon to key atom bonds, such as tributylarsine, pentaphenylantimony; (B) compounds having one carbon to key atom bond in which the remaining valences of the key atom are taken up by hydrogen or halogen atoms or hydroxyl groups, such as octyl arsine, phenylarsine sesquisulphide, triphenyl stibine iodide cyanide, and tetrabutylarsonium hydroxide; (C) compounds having up to three direct bonds between carbon and key atoms and at least one double bond from the key atom to oxygen or sulphur, such as tributylarsine sulphide; (D) compounds having in addition to the carbon to key atom link both a double bond to oxygen or sulphur and a bond from the key atom to a halogen atom or hydroxyl group, such as phenyl dichloroarsine oxide; (E) compounds having in addition to the key atom to carbon bond the remaining valences occupied by bonds to oxygen, sulphur, nitrogen or phosphorus linking organic radicals to the key atom, such as butyldioctoxyarsine; (F) compounds having two or more key atoms which may or may not be bonded together and have in addition to the key atom to carbon bond also bonds to hydrogen halogen, oxygen, sulphur, nitrogen or phosphorus such as bis (dibutylarsenic) oxide. Many more specific compounds in each class are given. In Examples, foams are prepared by reacting an adipic acid/1, 2, 6-hexanetriol polyester, toluene-2, 4- and 2, 6-diisocyanates and water in the presence of an emulsifying agent and (A) tri-n-butylstibine oxide; (B) tri-n-butylarsine oxide; (C) (for comparison) N-methylmorpholine. In alternative polyisocyanates of the formula R(NCY)x where x is two or more, R can be hydrocarbon or of the type -R-Z-R- where Z is, for example, -O-, -OR-O, -CO-, -CO2-, -S-, -S-R-S, or SO2. Examples include 1, 8-diisocyanato-p-menthane, xylylene diisocyanates, (OCNCH2CH2OCH2)2, xylylene-a , a '-diisothiocyanate and isopropylbenzene-alpha-4-diisocyanate, polymeric diisocyanates and compounds of the formula M(NCY)x in which x is a monofunctional atom or group, such as ethylphosphonic diisocyanate, phenylphosphorous diisocyanate, compounds containing a Si-NCY group, and isocyanates derived from sulphonamides. As compounds containing active hydrogen there can