The methoxyl group is a common functional group widely present in many organic compounds, including natural products such as lignin and synthetic materials such as polymers. The following is a commonly used method for determining the methoxyl content:
principle
The determination of methoxy content is based on the action of methoxy and sodium sulfate to generate sulfate under acidic conditions, and then convert sulfate to sulfur dioxide through a stoichiometric reaction, measure the amount of sulfur dioxide generated, and calculate the methoxy content.
Instruments and Reagents
Sodium Sulfate: Use sodium sulfate with a purity of 99% or better.
Nitric acid: Use nitric acid with a purity of 65% or higher.
Ammonium molybdate: Use ammonium molybdate with a purity of 99% or higher.
Methanol: Use methanol with a purity of 99% or higher.
Acetone: Use acetone with a purity of 99% or better.
Methoxy standard: Use a methoxy standard with a purity of 99% or greater.
Cuvette: A certain quality cuvette can be obtained through washing, drying and weighing.
UV-Vis Spectrophotometer or Colorimeter.
Steps
Prepare the sample: Add about 0.1 g of the sample into 10 mL of sodium sulfate-nitric acid mixture, heat and react in a Water Bath for 1-2 hours, so that the methoxy group in the sample is completely converted into sulfate.
Add ammonium molybdate: After the reaction solution cools down to room temperature, add 10 mL of ammonium molybdate test solution, stir evenly with a magnetic stirrer, and let stand for 15-20 minutes to allow the reaction to fully proceed.
Adding methanol: Add 10 mL of methanol to the reaction solution, mix well, and filter the solution.
Determination of absorbance: take an appropriate amount of filtrate, add appropriate amount of acetone and mix evenly, use a UV-visible Spectrophotometer or Colorimeter to measure the absorbance of the solution at a wavelength of 20 nm. Simultaneously measure the absorbance of the methoxyl standard substance, and calculate the methoxyl content in the sample according to the standard curve.
