Peri-naphthalenes

In organic chemistry, peri-naphthalenes are particular derivatives of naphthalene with the formula C10H6-1,8-X2.

General structure of a perinaphthalene, where R1 and R2 represent the substituents.

Owing to the rigidity of the naphthalene skeleton, these substituents on the 1- and 8-positions are constrained to be relatively close 2.5 Å, which is within the van der Waals radius for many atoms. In contrast, ortho-substituents pendant from a benzene ring are separated by about 3.3 Å.[1][2]

## Examples

Because of this unusual structural feature, many unusual compounds are derived from peri-naphthalenes. One example is 1,8-bis(dimethylamino)naphthalene, known as proton sponge because of its high affinity for protons. Its ammonium derivative has a pKa of 12.7.[3] The compound 1,8-bis(dimethylboryl)naphthalene is known as hydride sponge because of its high affinity for hydride. It solubilizes potassium hydride. Other distinctive compounds include the diphosphine 1,8-bis(diphenylphosphino)naphthalene (dppn) and the disulfide, both of which are ligand precursors.[1]

## Synthesis

Several peri-naphthalenes are prepared via nitrations. Nitration of naphthalene gives 1,8-dinitronaphthalene, which undergoes hydrogenation to the diamine. The diamine can also be produced by reaction of the 1,8-diol with ammonia at high temperatures. The peri-naphthalene 1-amino-naphthalene-8-sulfonic acid is a precursor to other peri-naphthalenes. It is prepared by nitration of naphthalene-1-sulfonic acid followed by reduction. Diazotization followed by loss of N2 gives the naphthosulfone. This species reacts with NaOH to give sequentially 1-hydroxynaphthalene-8-sulfonic acid and then the 1,8-diol.[4]

Four peri-naphthalene derivatives.

Certain perinaphthalene derivatives can be prepared from 1,8-dilithionaphthalene, which in turn is generated by dilithiation of 1-bromonaphthalene:[5]

C10H7Br + BuLi → C10H7Li + BuBr
C10H7Li + BuLi → C10H6Li2 \+ BuH

The deprotonation requires TMEDA.

## References

1. ↑ 1.0 1.1 Kilian, P.; Knight, F. R.; Woollins, J. D., "Synthesis of ligands based on naphthalene peri-substituted by Group 15 and 16 elements and their coordination chemistry", Coordination Chemistry Reviews 2011, volume 255, 1387-1413. doi:10.1016/j.ccr.2011.01.015
2. ↑ Balasubramaniyan, V. (1966). "Peri Interaction in Naphthalene Derivatives". Chemical Reviews 66 (6): 567–641. doi:10.1021/cr60244a001.
3. ↑ 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
4. ↑ Gerald Booth (2005). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_009. .
5. ↑ van Soolingen, J.; de Lang, R. J.; den Besten, R.; Klusener, P. A. A.; Veldman, N.; Spek, A. L.; Brandsma, L. (1995). "A Simple Procedure for the Preparation of 1,8-Bis(diphenylphosphino)naphthalene". Synthetic Communications 25 (11): 1741–1744. doi:10.1080/00397919508015858.

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