Formaldehyde Discussion Notes

Formaldehyde

• Formaldehyde is produced by oxidizing methanol (methyl alcohol).

• Other name: Methanal

Silver Nitrate Test (Tollens' Test)

• Used to test for formaldehyde.

• Uses Tollens' reagent, which contains silver ions ($Ag^+$).

• Silver ions ($Ag^+$) are reduced to metallic silver ($Ag$).

• Aldehydes are weak oxidizing agents and can be oxidized easily, reducing silver ions ($Ag^+$) to silver metal ($Ag$) simultaneously.

• Ketones cannot be oxidized using this test.

• Formaldehyde (an aldehyde) can be oxidized, forming a silver mirror precipitate.

Fehling's Test

• Another oxidation test for aldehydes.

• Aldehydes reduce complex copper(II) ($Cu^{2+}$) to complex copper(I) ($Cu^+$).

• The aldehyde is converted to its corresponding carboxylic acid.

• $Alcohol \rightarrow Aldehyde \rightarrow Carboxylic Acid$

• Copper(II) ($Cu^{2+}$ ) is converted to copper(I) oxide ($Cu_2O$), resulting in a color change from blue to dark red or brick red precipitate.

Nurse Test

• If formaldehyde is present in urine, it interferes with the test and can mitigate the red precipitate.

• Nurse list agent converts to red precipitate.

Henry's Test

• Add one drop of dilute aqueous solution of phenol to the distillate form of a sample (e.g., milk).

• Carefully add strong sulfuric acid ($H<em>2SO</em>4$) in a test tube. A bright crimson color indicates formaldehyde.

• Larger formaldehyde proportion: milky white zone above the ring.

• Acetaldehyde (from ethanol oxidation) gives an orange-yellow color.

• Formaldehyde: crimson color at a proportion of 1 part in 2000.

Fluoroglucinal Test

• Formaldehyde + fluoroglucinol = reddish-brown color complex.

Resorcinol Test

• Red zones, slightly violet in color, appear.

• Positive result for formaldehyde; other aldehydes may also react.

Reminisphenol Hydrazine Test

• Positive result: yellow to orange precipitate (aldehyde and ketone).

• Ethanol oxidation converts to acetaldehyde.

• Acetaldehyde (oxidized ethanol) can produce a yellow to orange precipitate.

• Not specific to formaldehyde.

Formalin

• Formalin is a common source of formaldehyde and is used for preservation (e.g., preserving specimens).

Formaldehyde Toxicity

• Can cause anemia and respiratory failure.

• Skin contact can cause hypersensitivity or dermatitis.

• Nephrology cases.

• High concentrations can cause necrosis.

• Minor irritation.

• Exposure can cause irritation to eyes, nose, and respiratory system.

• Possible bronchitis and pneumonia.

Ingestion Treatment

• Can cause acidosis.

• Treatment includes sodium bicarbonate, dilution with water or milk.

• Respiratory support is crucial.

• Check for endoscopy perforations.

Exposure Treatment

• Skin: soap and water.

• Eyes: flush with saline, oxygen, or respiratory support.

• Inhalation: flushing of ice with saline, oxygen, or respiratory support.