Initially produced from naphthalene in West Germany nearly one hundred years ago, phthalic anhydride is a chemical of major importance. The largest outlet for phthalic anhydride, accounting for around 50% of demand, is in the manufacture of plasticizers used in polyvinyl chloride polymers and copolymers. Polyester resins consume 15% of total phthalic anhydride production and alkyd resins a further 13%. Phthalic anhydride is irritating to eyes, skin, nose and throat, and excessive exposure can lead to sensitization and asthma. Molten phthalic anhydride will cause burns in contact with skin. Phthalic anhydride is stable but reacts with moisture to give an acid which can corrode metals, giving off hydrogen. Spills should be contained; small quantities of the anhydride can be neutralized with aqueous sodium bicarbonate prior to disposal, according to local regulations. Nearly 90% of phthalic anhydride is produced from o-xylene and 10% from naphthalene.