Potassium sodium tartrate is a chemical compound formed from sodium and potassium salts of tartaric acid. 

It appears as a translucent white crystalline powder, soluble in water, insoluble in alcohol.

What it is used for and where

It is a chemical compound known as Rochelle salt.

Food

Ingredient listed in the European food additives list as E337, acidity regulator and antioxidant.

Cosmetics

Buffering agent. It is an iingredient that can bring an alkaline or acid solution to a certain pH level and prevent it from changing, in practice a pH stabiliser that can effectively resist instability and pH change.

Safety

Tartaric acid (E 334), sodium tartrates (E 335), potassium tartrates (E 336), sodium potassium tartrate (E 337) and calcium tartrate (E 354) are authorised as food additives according to Regulation (EC) No 1333/2008 on food additives. The Panel established a group ADI for l(+)‐tartaric acid and tartrates (E 334-337 and E 354) of 240 mg/kg bw per day, expressed as tartaric acid, by applying the total uncertainty factor of 10 to the reference point of 3,100 mg sodium tartrate/kg bw per day (the highest dose tested), that is approximately 2,440 mg tartaric acid/kg bw per day. Accordingly, the current ADI of 30 mg/kg bw per day is withdrawn (1).

• Molecular Formula     KNaC₄H₄O₆ or C₄H₄KNaO₆
• Molecular Weight      210.16
• CAS  304-59-6
• UNII    P49F8NV7ES
• EC Number   206-156-8
• DSSTox ID  
• IUPAC  potassium;sodium;(2R,3R)-2,3-dihydroxybutanedioate
• InChl=1S/C4H6O6.K.Na/c5-1(3(7)8)2(6)4(9)10;;/h1-2,5-6H,(H,7,8)(H,9,10);;/q;2*+1/p-2/t1-,2-;;/m1../s1
• InChl Key      LJCNRYVRMXRIQR-OLXYHTOASA-L
• SMILES  C(C(C(=O)[O-])O)(C(=O)[O-])O.[Na+].[K+]
• MDL number  MFCD00150989
• PubChem Substance ID    24853005
• ChEBI  63019
• NCI    C80954
• Nikkaji       J2.573I   

Synonyms:

• Rochelle's salt
• Seignette salt

References_____________________________________________________________________

(1) EFSA Panel on Food Additives and Flavourings (FAF); Younes M, Aquilina G, Castle L, Engel KH, Fowler P, Frutos Fernandez MJ, Fürst P, Gürtler R, Gundert-Remy U, Husøy T, Mennes W, Shah R, Waalkens-Berendsen I, Wölfle D, Boon P, Tobback P, Wright M, Aguilera J, Rincon AM, Tard A, Moldeus P. Re-evaluation of l(+)-tartaric acid (E 334), sodium tartrates (E 335), potassium tartrates (E 336), potassium sodium tartrate (E 337) and calcium tartrate (E 354) as food additives. EFSA J. 2020 Mar 11;18(3):e06030. doi: 10.2903/j.efsa.2020.6030.