Esters are less reactive than acid halides and anhydrides. In esterifications and acylations, pyridine activates the carboxylic acid halides or anhydrides. Organoantimony compounds are typically prepared by alkylation of antimony halides with Grignard reagents. These include oxides, sulfides, nitrides, and halides. Two common methods of elimination reactions are dehydrohalogenation of alkyl halides and dehydration of alcohols. The chemistry of acid halides and anhydrides is similar. Most preparations entail reactions of hydride donors with boron halides or alkoxides. Methanol is the precursor to most simple methylamines, methyl halides, and methyl ethers. Many sulfonic acids are prepared by hydrolysis of sulfonyl halides and related precursors. Hydrogen iodide, like other hydrogen halides, is toxic. The Appel reaction is also useful for preparing alkyl halides. It is a strong oxidising agent, reacting with sulfur, phosphorus, phosphorus halides, and potassium borohydride. Even aryl halides participate in this reaction. Primary and secondary phosphines are generally prepared by reduction of related phosphorus halides or esters. This transformation include alkylations with other classes of activated alkyl halides of synthetic interest.