Novel ionic liquid catalysts comprising terephthalate anions are capable of promoting the neutral hydrolysis of relatively large flake sizes of poly(ethylene terephthalate) at 0.5 mol% loading (200 °C, 4 h, 94% yield) without either attendant product inhibition or product contamination by protonated catalyst. Catalysts with large, lipophilic phosphonium cations outperform more polar variants.