Choline hydrogen carbonate

Boiling point

Description of key information

Boiling point / Decomposition temperature: ca. 300 °C at 1013 mbar (OECD 103, differential thermal analysis, Choline chloride)
Decomposition temperature: 302 – 305 °C (Choline chloride)
Decomposition temperature: 305 °C (Choline chloride)
Decomposition temperature: 50 °C (Sodium hydrogen carbonate)
In summary: Boiling point of the pure compound cannot be determined because the substance is expected to decompose before boiling, decomposition temperature: approx. 50 °C (NaHCO3) to 300 °C (Choline chloride)

Additional information

The Key study on Choline chloride (BASF, 1983) was performed equivalent to OECD Guideline 103 using differential thermal analysis (DTA) and was classified as Klimisch 2. Hence, the results can be considered as reliable. However, the nature of the test method does not allow to differentiate between boiling point and decomposition temperature, so cannot be clearly determined in general whether the subsequent exothermal reaction with a maximum at 300 °C (starting at 250 °C) is attributed to boiling or decomposing. Hence, two additional supporting values gained from Choline chloride were taken from peer-reviewed databases. Here, it is stated clearly that Choline chloride decomposes at 302 - 305 °C (GESTIS, 2013) resp. 305 °C (HSDB 2013 / Lide, D.R., 1994), which allow to draw the conclusion that the examined exothermal reaction was attributed to decomposition rather than boiling.

All three sources on Choline chloride were classified as Klimisch 2, and the results can be generally considered to be reliable. Furthermore, all values are in the same small range (300 °C - 305 °C), which can be easily explained by the possible presence of minor impurities, differences due to different determination methods or generally by a certain margin of error accompanying all experimental determinations. Hence, the results are consistent. Since and it is scientifically expectable that decomposition will not take place on the single chloride ion but rather on the organic cation choline, which is identical to the one of Choline hydrogen carbonate, it can be assumed that decomposition of the pure choline cation will occur within the same temperature range. Therefore, the results gained with Choline chloride can be transferred to the pure choline cation.

 

However, the inorganic anion bicarbonate is thermo-labile, too, and has to be regarded for composition, too. Relevant information is provided in the supporting study on Sodium bicarbonate; the data therein was taken from a peer-reviewed database / handbook and are therefore considered as reliable. Since the anion in Sodium bicarbonate is identical to the one in Choline bicarbonate, and it can be reasonably concluded that decomposition will not occur on the single sodium ion but on the anion bicarbonate, the decomposition temperature of NaHCO3 (50 °C) can be used to support the conclusion that Choline bicarbonate decomposes before boiling.

 

So, in summary, the boiling point of pure Choline hydrogen carbonate cannot be determined. According to REACH Annex VII section 7.3 Column 2, it is stated that the boiling point does not need to be determined if the substance decomposes before boiling. So, no datagaps were determined, and no further testing on the pure Choline carbonate is required.

 

The 75 % aqueous solution of Choline hydrogen carbonate is the predominantly available form on the market, and should hence be included in risk assessment, too. Since the boiling point of pure water is 100 °C, which is below the decomposition temperature of the cation, but way above the decomposition temperature of the bicarbonate, it can be reasonably concluded that also the aqueous solution will not boil prior to the decomposition of Choline carbonate. Furthermore, the boiling point of the solution, which is related to the one of pure water, only describes the phase transition of the solvent water, and is therefore less relevant for the registered substance Choline bicarbonate.

 

So, sufficiently reliable data regarding the boiling points / decomposition temperature of both relevant forms of Choline hydrogen carbonate is available, no datagaps were identified and the tonnage driven data requirement under REACH are fully met.