p-Anisidine (or para-anisidine) is a white solid with the formula CH3OC6H4NH2, commercial samples can appear grey-brown owing to air oxidation.

Anisidine value

p-Anisidine condenses readily with aldehydes and ketones to form Schiff bases, which absorb at 350 nm. This colorimetric reaction is used to test for the presence of oxidation products in fats and oils, an official method for detecting them by the American Oil Chemists' Society. It is particularly good at detecting unsaturated aldehydes, which are the ones that are most likely to generate unacceptable flavors, making it particularly useful in food quality testing.

Natural Occurrence

p-Anisidine is a polyphenol compound found in foods of plant origin.

Applications in Chemical Detection

In the detection and quantification of copper(III) ions, p-Anisidine plays a crucial role as a reagent, facilitating the formation of a distinctive colored complex. When 0.2% aqueous p-Anisidine is introduced to copper(III) solutions in the presence of 0.03N acetic acid, an immediate formation of a stable pink-colored product occurs. This reaction is pivotal for its applicability in detecting the presence of copper(III) ions in various samples. The distinct color change serves as a visual indicator of the presence of copper(III), enabling rapid qualitative analysis. Furthermore, the spectrophotometric determination of copper(III) using p-Anisidine involves measuring the absorbance of the resulting colored complex at a specific wavelength. In this case, the wavelength of maximum absorption is determined to be 533 nm. This characteristic absorption peak allows for quantitative analysis of copper(III) concentrations in solution. The application of Beer's law in this context indicates that the formation of the colored complex between p-anisidine and copper(III) follows a linear relationship within a certain concentration range.¹

Toxicity

P-Anisidine is a relatively toxic compound with a permissible exposure limit of 0.5 mg/m3. It can irritate the skin and eyes causing a rash orburning feeling on contact.

Breathing p-Anisidine can irritate the nose and throatcausing coughing and wheezing.High levels can interfere with the ability of the blood tocarry Oxygen causing headache, fatigue,dizziness，and ablue color to the skin and lips (methemoglobinemia).Higher levels can cause trouble breathing,collapse andeven death.

Reference

1. Murthy NK, Murthy BS. Detection and spectrophotometric determination of copper(III) with p-anisidine. Talanta. 1995; 42(1): 101-103.