RESEARCH ARTICLE

 

A coloured spin trap which works as a pH sensor

 

 

Petre Ionita^*

Institute of Physical Chemistry, 202 Spl. Independentei, Bucharest 060021, Romania

 

 

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ABSTRACT

Nitration of 4-hydroxybenzaldehyde afforded 2,6-dinitro-4-hydroxybenzaldehyde 2, which in the presence of thionyl chloride is converted to 4-chloro-2,6-dinitrobenzaldehyde 3. This compound is very reactive towards nucleophiles, and reacts easily with methoxyamine, affording the intermediate 4-aminomethoxy-2,6-dinitrobenzaldehyde 4. Reaction of 4 with N-t-butyl-hydroxylamine led to a new spin trap of the nitrone type, namely 4-aminomethoxy-3,5-dinitrophenyl-1-f-butylnitrone 6. The spin-trapping capabilities of the new compound have been tested in a classical system, in which short-lived radicals were generated by irradiation. The new compound 6 contains an acidic proton with a pK_a value of 7.8, and removal of this by a base induces a colour change, from yellow to green-blue. In a similar way, a new stable nitronyl-nitroxide radical 8 has been obtained from the intermediate 4.

Keywords: Synthesis; free radical; spin-trapping; pH sensor; nitrone

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Full text available only in pdf format.

 

Acknowledgement

Financial support from GAR 45/2008 is acknowledged.

 

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Received 9 January 2008
Revised 21 July 2008
Accepted 10 October 2008

 

 

* E-mail: pionita@icf.ro