Editing Azulene (section)

==Derivatives==

1-Hydroxyazulene is an unstable green oil and it does not show [[keto–enol tautomerism]].<ref>{{cite journal | last =  Asao | first = Toyonobu | author2 = Shunji Ito | author3 =Noboru Morita  |title = 1-Hydroxyazulene and 3-hydroxyguaiazulene: Synthesis and their properties | journal = [[Tetrahedron Letters]] | year = 1989 | volume = 30 | issue = 48 | pages = 6693–6696 | doi = 10.1016/S0040-4039(00)70653-8 }}</ref>  2-Hydroxyazulene is obtained by hydrolysis of 2-methoxyazulene with hydrobromic acid. It is stable and does show keto–enol tautomerism.<ref name="2- and 6- hydroxyazulene">{{cite journal | last = Takase | first = Kahei | author2 = Toyonobu Asao | author3 =Yoshikazu Takagi | author4 = Tetsuo Nozoe |title = Syntheses and some properties of 2- and 6-hydroxyazulenes | journal = [[Chemical Communications]] | year = 1968 | issue = 7| pages = 368b–370 | doi = 10.1039/C1968000368B }}</ref> The [[pKa|p''K''<sub>a</sub>]] of 2-hydroxyazulene in water is 8.71. It is more acidic than [[phenol]] or [[naphthol]].  The p''K''<sub>a</sub> of 6-hydroxyazulenes in water is 7.38 making it also more acidic than phenol or naphthol.<ref name="2- and 6- hydroxyazulene" />

In naphth[''a'']azulene, a [[naphthalene]] ring is condensed at the 1,2-positions of azulene. In one such system<ref>{{cite journal | doi = 10.1021/jo051409f| pmid = 16238325| title = Novel Synthesis of Benzalacetone Analogues of Naphth[''a'']azulenes by Intramolecular Tropylium Ion-Mediated Furan Ring-Opening Reaction and X-ray Investigation of a Naphth[1,2-''a'']azulene Derivative| journal = [[The Journal of Organic Chemistry]]| volume = 70| issue = 22| pages = 8902–6| year = 2005| last1 = Yamamura| first1 = Kimiaki| last2 = Kawabata| first2 = Shizuka| last3 = Kimura| first3 = Takatomo| last4 = Eda| first4 = Kazuo| last5 = Hashimoto| first5 = Masao}}</ref> deviation from planarity is found, similar to that of [[helicene|tetrahelicene]].

[[Guaiazulene]] (1,4-dimethyl-7-isopropylazulene) is an alkylated derivative of azulene with an almost identical intensely blue colour. It is commercially available to the cosmetics industry where it functions as a skin conditioning agent.