Single-walled carbon nanotubes (SWNTs) were functionalized with alkyl and aryl groups using lithium in ethylenediamine under moderate conditions. This Benkeser reaction was convenient and scalable because no liquid ammonia was used. Raman, infrared spectra, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis as well as UV-vis-NIR spectra were used to characterize the functionalized SWNTs.