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Why does formaldehyde exist mainly in hydrated form in water?

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oxidation of alcohols — aldehyde Alcohols may be oxidized to give aldehydes, ketones, and carboxylic acids. The oxidation of organic compounds generally increases the number of bonds from carbon to oxygen, and it may decrease the number of bonds to hydrogen.

Formaldehyde exists in an aqueous solution primarily in a hydrated form, known as methanediol or methylene glycol, because of the high reactivity of its carbonyl group.1

In water, formaldehyde ( $H C H O$ ) undergoes a reversible nucleophilic addition reaction where a water molecule attacks the electrophilic carbon atom of the carbonyl group. This process results in the formation of an aldehyde hydrate with the general formula $R C H (O H)_{2}$ , which in the case of formaldehyde is $C H_{2} (O H)_{2}$ . Because the carbonyl carbon in formaldehyde is particularly susceptible to such attacks, the equilibrium in an aqueous environment heavily favors the formation of this stable hydrate over the free gaseous form. This aqueous mixture is commonly sold as formalin, a 37 percent solution of formaldehyde in water.123