- Title
- Synthesis of 2,4-Xylidine in continuous flow systems
- Creator
- Sagandira, Mellisa Brenda
- Subject
- Chemistry, Physical and theoretical -- Research
- Subject
- Chemistry
- Date Issued
- 2020
- Date
- 2020
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/49270
- Identifier
- vital:41616
- Description
- The continuous flow synthesis of 2,4-xylidine, an important compound in the fine chemical, pharmaceutical as well as the dyes and pigments industries was investigated in this study utilizing 1,3-dimethylbenzene as starting material. The first step involves the highly exothermic nitration of 1,3-dimethylbenzene with mixed acid to afford two nitro isomers, namely 1,3-dimethyl-2-nitrobenzene and 2,4-dimethyl-1-nitrobenzene. Since 2,4-xylidine is the targeted isomer, it is important to get a higher proportion of its nitration precursor 2,4-dimethyl-1-nitrobenzene. A safe and efficient synthesis of 2,4-dimethyl-1-nitrobenzene was therefore developed in continuous flow. This was aided by the micro reactor’s large surface area-to-volume ratio, one of the many features of continuous flow synthesis that enable rapid dissipation of heat allowing exothermic reactions to be conducted safely at ambient or higher temperatures. Two nitration protocols were developed using different micro reactors, a sonicated 1 ml PTFE tube reactor and 2 ml Uniqsis chip reactor. Using a sonicated PTFE tube reactor at room temperature and 15 min residence time, 2,4-dimethyl-1-nitrobenzene was afforded in 100 % conversion and 80 % selectivity. An increase in selectivity to 95 % and 90 % conversion towards 2,4-dimethyl-1-nitrobenzene was achieved using a 2 ml Uniqsis chip reactor at room temperature in 6 min residence time. This was accounted for due to efficient mixing of the two phases brought about by the reactor’s mixing structures, which are designed to create turbulent mixing. Scale-up synthesis of 2,4-dimethyl-1-nitrobenzene was conducted in a 4.5 ml LTF-XXL-ST-04 reactor at room temperature and 6 min residence time affording 90 % conversion and 95 % selectivity with a throughput of 16.6 g/h. Subsequently, reduction of 2,4-dimethyl-1-nitrobenzene to afford 2,4-xylidine was investigated in a 1 ml PTFE tube reactor (0.8 mm ID) using hydrazine in the presence of iron (III) 2,4-pentanedionate catalyst. Maximum conversion of 75 % was achieved at 170 °C in 15 min residence time. A more efficient reduction protocol was developed in a 2.7 ml packed column reactor (10 mm ID) using hydrazine in the presence of Pd/C at 50 °C and 2.5 min residence time affording 94 % conversion towards 2,4-xylidine. Lastly, multistep synthesis of 2,4-xylidine was performed using optimum conditions found using the 2 ml Uniqsis chip reactor and 2.7 ml packed column reactor with the incorporation of a phase separator. Joining the two reactors into a single continuous step afforded 100 % conversion and 95 % selectivity towards 2,4-xylidine with 8 min total residence time. Nitration of other organic compounds followed by reduction of the resultant nitro products was also investigated under respective optimum conditions determined for nitration of 1,3-dimethylbenzene and reduction of 2,4-dimethyl-1-nitrobenzene.
- Format
- x,109 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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NMU School of BioMolecular and Chemical Sciences
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Sagandira, M.pdf | 3 MB | Adobe Acrobat PDF | View Details Download |