Background: Four members of N,N-disulfo-1,1,3,3-tetramethylguanidinium chlorometallates
[DSTMG]n[X], where n= 1 or 2; X= FeCl4
2- were synthesized as solid
Brønsted-Lewis acidic compounds and studied the catalytic activity with the most acidic salt for threecomponent
synthesis of 1,2-dihydro-1-aryl-3H-naphth[1,2-e][1,3]oxazin-3-ones.
Methods: N,N-disulfo-1,1,3,3-tetramethylguanidinium chlorometallates of the four transition metal
cations such as Fe(III), Zn(II), Ni(II) and Mn(II) were prepared after treatment of the parent ionic liquid
N,N-disulfo-1,1,3,3-tetramethylguanidinium chloride [DSTMG][Cl] with the respective metal
chlorides in different mole fractions at 75 ºC. The synthesis of 1,2-dihydro-1-aryl-3H-naphth[1,2-
e][1,3]oxazin-3-ones was carried out via three-component reaction of 2-naphthol, aromatic aldehydes
and urea under neat condition at 90 ºC using 7 mol% of the [DSTMG][FeCl4] catalyst.
Results: The characterization of synthesized chlorometallates was done using spectroscopic and other
analytical techniques, including thermogravimetric analysis and Hammett acidity studies. Among the
four salts, the salt of Fe(III) ion was observed as the strong Brønsted acidic hydrophobic salt and thus
chosen for the catalytic study.
Conclusion: A new type of chlorometallates of guanidinium cation with composition [DSTMG]n[X],
where X= FeCl4
2- and n= 1 or 2 were developed as –SO3H functionalized
solid acids with varied thermal stability (150-250 ºC) and physisorbed water (0-20%) as observed
from the thermogravimetric study. From them, the most Brønsted acidic Fe(III) salt was employed as
an efficient recyclable heterogeneous catalyst for the one-pot synthesis of 1,2-dihydro-1-aryl-3Hnaphth[
1,2-e][1,3]oxazin-3-ones in neat condition.