1,8-Bis(dimethylamino)naphthalene

Structure and properties

This compound is a diamine in which the two dimethylamino groups are attached on the same side (peri position) of a naphthalene ring. This molecule has several very interesting properties; one is its very high basicity; another is its spectroscopic properties.

With a pK of 12.34 Additionally, although many aromatic amines such as aniline show reduced basicity (due to nitrogen being sp2 hybridized; its lone pair occupying a 2p orbital and interacting and being withdrawn by the aromatic ring), this is not possible in this molecule, as the nitrogens' methyl groups prevent its substituents from adopting a planar geometry, as this would require forcing methyl groups from each nitrogen atom into one another—thus the basicity is not reduced by this factor which is found in other molecules. It is sterically hindered, making it a weak nucleophile. Because of this combination of properties, it has been used in organic synthesis as a highly selective non-nucleophilic base.

Proton sponge also exhibits a very high affinity for boron and is capable of displacing hydride from borane to form a boronium–borohydride ion pair.

Preparation

This compound is commercially available. It may be prepared by the methylation of 1,8-diaminonaphthalene with iodomethane or dimethyl sulfate.

Related compounds

Other proton sponges

Second generation proton sponges are known with even higher basicity. 1,8-bis(hexamethyltriaminophosphazenyl)naphthalene or HMPN is prepared from 1,8-diaminonaphthalene by reaction with tris(dimethylamino)bromophosphonium bromide in the presence of triethylamine. HMPN has a pK of 29.9 in acetonitrile which is more than 11 orders of magnitude higher than Proton Sponge.

The aromatization of an additional ring in 4,12-Dihydrogen-4,8,12-triazatriangulene is utilized by Al-Yassiri and Puchta to get a representative for a new class of Δ-shaped proton sponges. This compound has a calculated proton affinity of 254 kcal/mol (B3LYP/6-311+G**) and is therefore between 1,8-Bis(dimethylamino)naphthalene and HMPN.

Hydride sponge

The chemical inverse of a proton sponge would be a hydride sponge. This property is exhibited by CH(BMe), which reacts with potassium hydride to afford K[CH(BMe)H].

References

References

1. R. W. Alder. (1968). "The remarkable basicity of 1,8-bis(dimethylamino)naphthalene". [[Chem. Commun.]].
2. I. Kaljurand, A. Kütt, L. Sooväli, T. Rodima, V. Mäemets, I. Leito, I. A. Koppel. Extension of the Self-Consistent Spectrophotometric Basicity Scale in Acetonitrile to a Full Span of 28 p''K''{{sub. a Units: Unification of Different Basicity Scales. ''J. Org. Chem.'', '''2005''', ''70'', 1019–1028. {{doi. 10.1021/jo048252w
3. R. W. Alder. (1989). "Strain effects on amine basicities". [[Chem. Rev.]].
4. Alexander F. Pozharskii and Valery A. Ozeryanskii "Proton sponges and hydrogen transfer phenomena" Mendeleev Commun., 2012, 22, 117–124. {{doi. 10.1016/j.mencom.2012.05.001
5. (2014-08-28). "Lewis base activation of borane–dimethylsulfide into strongly reducing ion pairs for the transformation of carbon dioxide to methoxyboranes". Chemical Communications.
6. Vladimir I. Sorokin. (2003). "A Simple and Effective Procedure for the ''N''-Permethylation of Amino-Substituted Naphthalenes". European Journal of Organic Chemistry.
7. Volker Raab. (2005). "1,8-Bis(hexamethyltriaminophosphazenyl)naphthalene, HMPN: A Superbasic Bisphosphazene "Proton Sponge"". [[Journal of the American Chemical Society.
8. Muntadar A. H. Al-Yassiri. (2023). "Predicting a New Δ-Proton Sponge-Base of 4,12-Dihydrogen-4,8,12-triazatriangulene through Proton Affinity, Aromatic Stabilization Energy, and Aromatic Magnetism". [[ChemPhysChem]].
9. (1985). "Hydride sponge: 1,8-naphtalenediylbis(dimethylborane)". Journal of the American Chemical Society.