Green Synthesis of Sodium Cyanide Using Hydrogen Cyanide Extracted under Vacuum from Cassava (<i>Manihot esculenta</i> Crantz) Leaves

Abstract

This study was carried out to develop a green approach to synthesising sodium cyanide (NaCN) using hydrogen cyanide (HCN) extracted from cassava (Manihot esculenta Crantz) leaves after 120 min of maceration at 30 °C and 45 min of recovery under vacuum at 35–40 °C. The CN- ion released via autolysis was reacted with the Na+ ion following vacuum extraction of the former to produce NaCN by saturating the absorbing sodium hydroxide (NaOH) solution. This specific extraction method avoided direct contact between the cassava leaves homogenate and the absorbing solution. NaCN was crystallised by drying the NaCN slurry at 100 °C in an air oven. A total of 15.70 kg of fresh cassava leaves was needed to produce 32.356 g of NaCN (green-NaCN) (% NaCN yield = 0.21%). The results of X-ray diffraction, attenuated total reflectance–Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy, show that NaCN was successfully prepared using the proposed method. These spectral techniques showed that the control and green-NaCN contained sodium carbonate impurities. The latter was quantified by the titration experiments and was found to be 0.61% and 2.29% in the control and green-NaCN, respectively. Furthermore, the titration experiments revealed that the residual NaOH content was 1.63% in control NaCN and 4.68% in green-NaCN. The aim of modifying the green synthesis route for producing NaCN from cassava, developed by the Attahdaniel research group in 2013 and 2020, was achieved.

Keywords

• green synthesis
• sodium cyanide
• hydrogen cyanide
• cassava
• cyanogenic glucoside
• linamarin