kyl group, and X2 is a halogen atom such as a chlorine atom, a bromine atom or an iodine atom, a mercury type preservative such as phenylmercury nitrate, phenylmercury acetate and thimerosal; a surfactant type preservative such as benzalkonium chloride and pyridinium bromide; an alcohol type preservative such as chlorohexyzine, polyhexamethylene biguanide and chlorobutanol; methylparaben, propylpa