SI contained 1 mole of formaldehyde per mole of HMSI (%CH2Ocalc = 23.3, %CH2Ofound = 23.2). It was also found that upon addition of 1 mole of EO to HMSI ca 0.3 mole of unstable bonded formaldehyde as O-(hydroxymethyl) groups remains, but after addition of 2 moles EO practically whole formaldehyde is blocked by oxirane. These results suggest, that either O-(hydroxymethyl) groups are formed as the result of partial dissociation of formaldehyde from N-(hydroxymethyl) groups of HMSI and then added to N-(hydroxyalkyl) group according to the scheme:
or first the oxirane is attached to N-(hydroxymethyl) group with formation of (IV), from which the formaldehyde is released and rearranged into the end of chain according to the scheme:
Cryoscopic determination of molar mass of HMSI in dioxane and DMSO indicated, that in both solvents the molar mass of HMSI was equal to calculated one (128.9 and 128.5 g/mol, respectively; calc. 129.1). This suggests that no dissociation of formaldehyde from N-(hydroxymethyl) groups occurs and the formaldehyde rearrangement takes place after blocking with oxirane (reaction 34). This corroborate well with our previous studies on the reaction of hydroxymethylated derivatives of uric acid with oxiranes . The system HMSI-TEA was also studied by cryoscopic method (Table 2). As in other cases the relation ce < ct, was kept valid, what confirms that dissociation of formaldehyde from alcoholate did not occur upon TEA.
It is not possible to define the character of the bond in adduct on the basis of cryoscopic measurements. Therefore the IR and 1H-NMR spectra were recorded. The IR spectrum of SI shows the valence band of NH at about 3200 cm–1 (Figure 2(b)). When 3-fold excess of TEA was added, the band disappeared (Figure 2(d)) accom-panied by appearance of weak band from ammonium cation (C2H5)3NH+ in the region 2300 - 2500 cm–1. Undo-ubtedely, the proton transfer to TEA from imide took place. This band was more pronounced in the mixture of HESI and TEA (Figures 2(c) and (e)). The spectral features were: the disappearance of hydroxyl valence band at 3500 cm–1, and simultaneous appearance of absorption at 2400 cm–1. Thus, the product of reaction can also be the proton donor, which agrees well with cryoscopic data.
IR spectra rather preclude the formation of hydrogen bonded adduct; in such a case the broadening of the N-H
Figure 2. The relevant region of IR spectrum of TEA (a), SI (b), HESI (c), and mixtures of TEA with SI (d) and HESI (e).
band should be observed, while only the disappearance was the case. 1H NMR spectra provide further evidences on the presence of ion pair. Addition of TEA to imide solution in DMSO-d6 resulted in disappearance of imide group proton resonance >NH and simultaneous grow of resonance from (C2H5)3NH+ cation shifted upfield. The resonances are separated by 4.2 ppm in SI/SI-TEA system and by 6.1 ppm PI/PI-TEA. This spectroscopic picture also indicates the formation of ion pair instead of hydrogen bonding. Individual chemical shifts for the system SI/SI-TEA and PI/PI -TEA are as below:
SI (2.8, 4H, CH2; 11.4, 1H, NH); SI/TEA ( 1.05, 9HCH3; 2.55, 6H, CH2 from TEA, 2.8, 4H, CH2 from SI; 7.2, 1H, NH+).
PI (7.8, 4H, Ph; 11.6, 1H, NH); /PI-TEA (1.05, 9H, CH3; 2.55, 6H, CH2 from TEA, 7.8, 4H, Ph; 5.5, 1H, NH+).
4. Summary and Conclusions
1) Based upon experimental kinetic the mechanism of the reaction of cyclic imides and oxiranes was proposed and verified by instrumental and analytical methods.
2) The initial step of reaction is the formation of 1:1 imide: TEA adduct, which intermediates the proton transfer from imide to oxirane. The adducts could not be isolated, although their presence in solutions was demonstrated experimentally.
3) The crucial bond in adduct has ionic character; in non-aqueous solvents it is present as ion pair, while in water the adduct dissociate and free ions are present.
4) The suggested mechanisms can be applied in expalantion of first stages of obtaining of polyetherols in reaction of oxiranes with cyclic imides containg a couple of imide groups such as isocyanuric acid, parabanic acid and barbituric acid etc.