b -amino acylated derivatives of organic compounds containing acylatable hydroxy or mercapto groups are prepared by reacting the compound with a b -lactam unsubstituted at the ring nitrogen in the presence of hydrogen halide but in the absence of water. Specified hydroxy compounds are mono-, di-, or poly-hydric saturated or unsaturated, aliphatic or carbocyclic, alcohols containing 1-30 carbon atoms which may be substituted with chloro or alkoxy groups, steroid alcohols, partial ethers and esters of glycols and poly-glycols, hydroxy sulphones, hydroxyl-containing fatty oils, salts of amino alcohols and quaternary salts thereof and phenolic compounds. Mercapto compounds include alkyl mercaptans containing 1-20 carbon atoms and thiophenols. b -lactams utilisable include those of the general formula: <FORM:0961304/C1/1> wherein R1, R2 and R3 are a hydrogen atom, an alkyl radical containing 1-10 carbon atoms or R2 may be a phenyl or an alkylated phenyl radical. R4 represents an alkyl radical of 1-10 carbon atoms, a phenyl radical which may be substituted or the group -CH2-COO-CnH2nm where n is 1-20. Two of the radicals may form a cycloaliphatic ring and it is possible to have two b -lactam groups in the same molecule. Numerous lactams of this type are listed. It is stated that compounds of formula: <FORM:0961304/C1/2> obtained by this process are novel, wherein R is a saturated hydrocarbon radical of 9-22 carbon atoms, R1 and R2 are hydrogen or alkyl radicals and 1-6 carbon atoms and R3 and R4 are alkyl radicals the sum of the carbon atoms being at most 5. The reaction is normally effected from -5 to 100 DEG C. Inert solvents may be present and many are specified. The hydrogen halide may be the chloride, bromide, iodide or fluoride and the amino ester produced is normally obtained in the form of its hydrogen halide salt. The free esters may be liberated by treatment with alkalies suitably by adding the alkali to an organic solution of the ester salt. Specified alkalies include ammonia, alkyl metal amides, sodium alcoholates and sodium salts of malonic esters. Many examples are given of the aminoacylation of the specified hydroxy and mercapto compounds in benzene, dioxane or ether as solvents using b -methyl-b -butyrolactan, b -methyl-b -caprolactam or b -phenyl-b -propio-lactam in the presence of hydrogen chloride. Examples 8, 9, 11, 15 and 16 describe the formation of ureido esters by adding potassium cyanate to the amino ester salt.ALSO:b -amino acylated derivatives of polymeric materials containing acylatable hydroxy or mercapto groups are prepared by reacting the polymer with a b -lactam unsubstituted at the ring nitrogen in the presence of a hydrogen halide but in the absence of water. The polymeric material may be a liquid, usually dissolved in an inert solvent, or be in a solid form including foils and fibres. Specified polymers include polyglycols of molecular weight above 1,000, polyglycide, polymeric hydroxy methyl-oxacyclobutane, polyesters containing hydroxyl groups such as those from adipic acid, 1:4 butane diol and a minor amount of 1:2:5 trihydroxyhexane, and from terephthalic acid and ethylene glycol or 1:4 butane diol, hydroxylated polyamides e.g. linear polyureas prepared in tertiary butanol from N:N1 di-[-b -hydroxyethyl]-hexamethylene diamine and hexamethylene-di-isocyanate, phenol novalaks, hydroxyethylated novalaks, derivatives of polymeric carbohydrates such as partially esterified or etherified cellulose and starch, and hydroxylated polyvinyl compounds such as polyvinyl alcohol, partially saponified polyvinyl esters, partial polyvinyl acetals, polyallyl alcohol and partially saponified copolymers of vinyl acetate and ethylene. The products from polymeric hydroxyl compounds are stated to be novel. The reaction is normally effected from 5 to 100 DEG C. Inert solvents may be present and many are specified. The hydrogen halide may be the chloride, bromide, iodide, or fluoride and the amino ester produced is normally obtained in the form of its hydrogen halide salt. The free esters may be liberated by treatment with alkalies suitably by adding the alkali to an organic solution of the ester salt. Specified alkalies include ammonia, alkali metal amides, sodium alcoholates, and sodium salts of malonic esters. b -lactams utilisable include those of the general formula: <FORM:0961304/C3/1> wherein R1, R2 and R3 are a hydrogen atom, an alkyl radical containing 1-10 carbon atoms, or R2 may be a phenyl radical. R4 represents an alkyl radical of 1-10 carbon atoms, a phenyl radical which may be substituted or the group -CH2-COO-CnH2n+1 where n is 1-20. Two of the radicals may form a cycloaliphatic ring and it is possible to have two b -lactam groups in the same molecule. It is stated that the lactams may already be present in the solid polymers as plasticizers or softeners. The amino-acylated products have affinity for acid dyestuffs, for plasticizers containing carboxyl and particularly sulphonic ester or sulphonic semi-ester groups, for compounds having strongly acid phenolic groups, for chromic acid and for metal complex acids. Examples describe the amino acylation of (1) cellulose acetate in acetone by b -methyl-b -butyrolactam with hydrogen chloride present. (2) polyvinyl formal containing minor amounts of polyvinyl acetate and polyvinyl alcohol, and polyvinyl butyral containing 23% of polyvinyl alcohol by b -methyl-b butyrolactam or b -phenyl-b -propiolactam in methylene chloride with hydrogen chloride present, (3) methyl cellulose in methylene chloride by b -methyl-b -butyrolacta with hydrogen chloride present, (4) cellulose acetate in acetone by b -methyl-b -caprolactam with HF present (Example 27), the product in each case being cast into a film dyeable with acid dyestuffs.ALSO:b -amino acylated derivatives of dyestuffs containing acylatable hydroxy or mercapto groups are prepared by reacting the dyestuff with an hydrogen halide and a b -lactam unsubstituted on the ring nitrogen atom, in the absence of water. Specified dyestuffs are the azo dyes <FORM:0961304/C4-C5/1> and <FORM:0961304/C4-C5/2> the methine dyestuff <FORM:0961304/C4-C5/3> 1 - amino - 4 - [b - hydroxyethylamino] - anthraquinone, 1 - hydroxy - 4 - [b - hydroxyethylamino] - anthraquinone, leuco derivatives of vat dyestuffs and sulphur dyestuffs. The b -lactams utilizable include those of the general formula <FORM:0961304/C4-C5/4> wherein R1, R2 and R3 are an hydrogen atom, an alkyl radical containing 1-10 carbon atoms or R2 may be a phenyl radical. R4 represents an alkyl radical of 1-10 carbon atoms, a phenyl radical which may be substituted or the group -CH2-COO-CnH2n + 1, where n is 1-20. Two of the radicals may form a cycloaliphatic ring and it is possible to have two b -lactam groups in the same molecule. Numerous lactams of this type are listed. The reaction is normally carried out from - 5 to + 100 DEG C. Inert solvents may be present and many are specified. The hydrogen halide may be the chloride, bromide, iodide or fluoride and the amino ester produced is normally obtained in the form of its hydrogen halide salt. The free esters may be liberated by treatment with alkalies suitably by adding the alkali to an organic solution of the ester salt.