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A series of magenta azo dyes for use in inkjet printers have been synthesised in order to study the effects of substituted arylhydrazide substituents on their light and ozone fastness. Large-scale syntheses were successfully adapted to the laboratory and arylhydrazides were coupled to an existing azo dye via a cyanuric chloride coupling reaction in good yield and purity. Improved methodologies were developed for the synthesis of a series N-methylhydrazides, N,N’-dimethylhydrazides and N’-isopropylhydrazides. N-methylhydrazides were synthesised by reaction of methylhydrazine with an appropriate acid chloride. N.N’-dimethylhydrazides were synthesised from N-methylhydrazides, avoiding the use of the carcinogenic dimethylhydrazine employed in previous syntheses. Synthesis was via a reductive amination strategy employing previously unreported N-methyl, N’-methylidene arylhydrazides, followed by reduction with sodium cyanoborohydride. N’-isopropylhydrazides were also prepared via reductive amination, following condensation of commercially available hydrazides with propanone, again followed by reduction with sodium borohydride. The newly synthesised dyes were tested at Avecia (Blackley) for light and ozone fastness according to standard protocols. The N-methylhydrazides series of dyes showed slightly improved ozone fastness, light fastness was essentially unchanged across the range of dyes. Solution ozonolysis experiments were carried out on simple dye systems, such as 1-phenylazo-2-napthol and 1-phenylazo-4-napthol. In order to study the effects of azo / hydrazone tautomerism, some of the “locked” tautomers of these compounds were synthesised by methylation of the appropriate functional group. The main intermediate formed was napthoquinone. Solution ozonolysis was also performed on some of the more complex hydrazide substituted dyes previously synthesised and the rates of ozonolysis determined.