Peri-naphthalenes
In organic chemistry, peri-naphthalenes are particular derivatives of naphthalene with the formula C10H6-1,8-X2.
File:Perinaphtalene structure.png
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.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}}
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.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}} 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.
Synthesis
Several peri-naphthalenes are prepared via nitrations. Dinitration 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.{{Ullmann|author=Gerald Booth|title=Naphthalene Derivatives|year=2005|doi=10.1002/14356007.a17_009}}.
Certain perinaphthalene derivatives can be prepared from 1,8-dilithionaphthalene, which in turn is generated by dilithiation of 1-bromonaphthalene:{{cite journal|author=van Soolingen, J.|author2=de Lang, R. J.|author3=den Besten, R.|author4=Klusener, P. A. A.|author5=Veldman, N.|author6=Spek, A. L.|author7=Brandsma, L.|title=A Simple Procedure for the Preparation of 1,8-Bis(diphenylphosphino)naphthalene|journal=Synthetic Communications|year=1995|volume=25|issue=11 |pages=1741–1744|doi=10.1080/00397919508015858}}
:C10H7Br + BuLi → C10H7Li + BuBr
:C10H7Li + BuLi → C10H6Li2 + BuH
The deprotonation requires TMEDA.
References
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