Formate
# Formate

Formate (IUPAC name: methanoate) is the conjugate base of formic acid. Formate is an anion (HCO−2) or its derivatives such as ester of formic acid. The salts and esters are generally colorless.

## Fundamentals

When dissolved in water, formic acid converts to formate:

    $HCO_2H$ → HCO−2 + $H^+$

Formate is a planar anion. The two oxygen atoms are equivalent and bear a partial negative charge. The remaining C-H bond is not acidic.

## Biochemistry

Formate is a common C-1 source in living systems. It is formed from many precursors including choline, serine, and sarcosine. It provides a C-1 source in the biosynthesis of some nucleic acids. Formate (or formic acid) is invoked as a leaving group in the demethylation of some sterols. These conversions are catalyzed by aromatase enzymes using $O_2$ as the oxidant. Specific conversions include testosterone to estradiol and androstenedione to estrone.

Formate is reversibly oxidized by the enzyme formate dehydrogenase from Desulfovibrio gigas:

    HCO−2 → $CO_2$ + $H^+$ + 2 $e^−$

## Formate esters

Formate esters have the formula HCOOR (alternative way of writing formula ROC(O)H or $RO_2CH).$ Many form spontaneously when alcohols dissolve in formic acid.

The most important formate ester is methyl formate, which is produced as an intermediate en route to formic acid. Methanol and carbon monoxide react in the presence of a strong base, such as sodium methoxide:

    $CH_3OH$ + CO → $HCOOCH_3$

Hydrolysis of methyl formate gives formic acid and regenerates methanol:

    $HCOOCH_3$ → HCOOH + $CH_3OH$

Formic acid is used for many applications in industry.

Formate esters often are fragrant or have distinctive odors. Compared to the more common acetate esters, formate esters are less commonly used commercially because they are less stable. Ethyl formate is found in some confectionaries.

## Formate salts

Formate salts have the formula $M(O_2CH)(H_2O)_x.$ Such salts are prone to decarboxylation. For example, hydrated nickel formate decarboxylates at about 200 °C with reduction of the $Ni^{2+}$ to finely powdered nickel metal:

    $Ni(HCO_2)_2(H_2O)_2$ → Ni + 2 $CO_2$ + 2 $H_2O$ + $H_2$

Such fine powders are useful as hydrogenation catalysts.

## Examples

* ethyl formate, $CH_3CH_2(HCOO)$
* sodium formate, Na(HCOO)
* potassium formate, K(HCOO)
* caesium formate, Cs(HCOO); see Caesium: Petroleum exploration
* methyl formate, $CH_3(HCOO)$
* methyl chloroformate, $CH_3OCOCl$
* triethyl orthoformate
* trimethyl orthoformate, $C_4H_{10}O_3$
* phenyl formate $HCOOC_6H_5$
* amyl formate
