4,4'-Dimethyltriphenylamine

Chemical Properties

White to yellow solid

Uses

4,4'-Dimethyltriphenylamine (DMTPA) can be used as a starting material for the synthesis of 4-[bis(4-methylphenyl)amino]benzaldehyde (BMABA). BMABA is a molecule exhibiting mechanophluorescence, and it has applications in fields such as sensors, data storage and smart switches ^[5]. The reaction process and mechanism are as follows:
This synthesis method is carried out via the Vilsmeier-Haack reaction. DMTPA (1.37 g, 5.01 mmol) was dissolved in DMF (2.3 mL, 29.8 mmol), and trichlorooxaphosphorane (0.46 mL, 5.02 mmol) was slowly added under an ice-water bath. Upon completion of the addition, the reaction temperature was adjusted to 100 °C and the mixture was heated for 3 h. After cooling to room temperature, the product was dissolved in dichloromethane, then neutralised with a sodium bicarbonate solution, extracted, dried over anhydrous Na₂SO₄, and the solid product was collected by vacuum distillation. Chromatographic separation was performed on a silica gel column using a mobile phase of dichloromethane and methanol (Vdichloromethane:Vmethanol = 100:1), yielding pale yellow BMABA (1.14 g, 75.6% yield).

Synthesis

Bromobenzene (7.71 g, 49.1 mmol), 4,4'-dimethyldiphenylamine (9.78 g, 49.6 mmol), sodium tert-butoxide (5.70 g, 59.3 mmol), palladium acetate (110 mg, 0.490 mmol), tri-tert-butylphosphine (396 mg, 1.96 mmol), and o-xylene (110 mL) were added sequentially under nitrogen protection to a 200 mL three-neck flask equipped with a stirrer. 1.96 mmol) and o-xylene (110 mL). The reaction mixture was stirred at 120 °C for 20 hours. Upon completion of the reaction, 150 mL of pure water was added to the mixture to wash and separate the organic phase. Subsequently, the organic phase was washed with another 150 mL of pure water, followed by washing with saturated saline and separation. The resulting organic layer was concentrated under reduced pressure and the solvent was removed by distillation. The resulting residue was purified by silica gel column chromatography to give 12.9 g of the final white crystalline product 4,4'-dimethyltriphenylamine (96% yield, 99.1% purity).

Purification Methods

Crystallise the amine once from EtOAc, then twice from EtOH to give pale yellow needles [Marsden J Chem Soc 627 1937, Beilstein 12 III 2033.]

References

[1] Journal of the American Chemical Society, 2012, vol. 134, # 50, p. 20262 - 20265
[2] Patent: JP5966736, 2016, B2. Location in patent: Paragraph 0075; 0078
[3] Organic and Biomolecular Chemistry, 2009, vol. 7, # 19, p. 3922 - 3925
[4] Organic Letters, 2005, vol. 7, # 11, p. 2209 - 2211
[5] Yu-Zhen Pan. (2024). [Comprehensive undergraduate experiment: synthesis and chromism of 4-[bis(4-methylphenyl)amino] benzaldehyde]. Se Pu = Chinese Journal of Chromatography, 42 3, 304–308. https://doi.org/10.3724/SP.J.1123.2023.11009