# 2,5-Dihydroxy-1,4-benzoquinones Appended with −P(O)(OR)2 (R = Me or Et) Groups and Their Ammonium and Lithium Salts: Structural, Spectroscopic, and Electrochemical Properties

## TL;DR

This paper describes the synthesis and characterization of new benzoquinone compounds with phosphonato groups and their salts, highlighting their structural and electrochemical properties.

## Contribution

The first examples of anillic acids appended with −P(=O)(OR)2 groups and their salts are synthesized and characterized.

## Key findings

- Phosphonato groups increase the solubility of free acids and provide coordination/hydrogen bonding sites in their salts.
- Compounds and their salts were characterized using spectroscopic, electrochemical, and X-ray diffraction methods.
- The study reveals structural and electrochemical properties of these novel benzoquinone derivatives.

## Abstract

Synthetic methods yielding 2,5-dihydroxy-1,4-benzoquinones
appended
with dialkylphosphonato groups were established. Reactions of 1,4-dichloro-2,5-dihydroxybenzene
with dialkylchlorophosphates ClP­(O)­(OR)2 (R = Me
or Et) produced 1,4-dichloro-2,5-bis­(dimethylphosphato)­benzene (1a) and 1,4-dichloro-2,5-bis­(diethylphosphato)­benzene (1b). Low-temperature reactions of 1a–b with lithium diisopropylamide (2 equiv) proceeded with double
anionic phospho-Fries rearrangement, yielding 2,5-dichloro-3,6-bis­(dialkylphosphonato)-1,4-hydroquinones 2a–b. Oxidations of 2a–b with K2S2O8 under basic
conditions proceeded with the nucleophilic displacement of both chlorides
by the hydroxy groups. Acidification of the reaction mixtures led
to the isolation of 2,5-dihydroxy-1,4-benzoquinones appended with
two dimethylphosphonato (H2
3a) or diethylphosphonato
(H2
3b) groups. Reactions of H2
3a and H2
3b with excess NH3(aq) or with LiOH yielded salts (NH4)2
3a, (NH4)2
3b, Li2
3a, and Li2
3b. All compounds
were characterized by spectroscopic (FT-IR, FT-NMR (1H, 13C, and 31P)) methods and by high-resolution mass
spectrometry or elemental analyses. Both 2,5-dihydroxy-1,4-benzoquinones
H2
3a–b and their ammonium
and lithium salts were investigated by cyclic voltammetry. Compounds 2a, H2
3a, H2
3b, and salts (NH4)2
3a·H2O, (NH4)2
3b·2H2O, Li2
3a·2H2O, and
Li2
3b were characterized by single-crystal
X-ray diffraction methods. Compounds H2
3a/H2
3b and their salts represent the first examples
of anillic acids appended with −P­(O)­OR2 groups.
Phosphonato functionalities were shown to be important factors in
increasing the solubility of free acids as well as providing coordination/hydrogen
bonding sites in their salts.