L-(+)-Tartaric Acid

L( )-tartaric acid (L-( )-Tartaric Acid,CAS No. 87-69-4), systemically named (2R,3R)-2,3-dihydroxysuccinic acid, molecular formula cis h o, relative molecular mass 150.09. It is the only naturally occurring and most commercially valuable form of the four stereoisomers of tartaric acid, the other three being D(-)-tartaric acid, DL-tartaric acid (racemate) and meso-tartaric acid (meso).

1. stereochemical characteristics
The tartaric acid molecule contains two identical chiral carbon atoms (C2 and C3), and this unique structure makes it a classical model compound for stereochemical studies. In 1848, the French chemist Louis Pasteur (Louis Pasteur) for the first time through the manual separation of sodium ammonium tartrate enantiomer crystals, found the molecular chiral phenomenon, laid the foundation of stereochemistry.

1. L( )-tartaric acid (natural type)
-Absolute configuration:(2R,3R)
-Optical activity: dextrorotatory, specific rotation [α] D²⁰= 12.0 ° to 12.8 °(c = 20, H₂ O)
-Physical properties: colorless transparent prismatic crystal or white crystalline powder, melting point 168-172 ℃, density 1.7598g/cm³(20 ℃)
-Solubility: highly soluble in water (139g/100 mL at 20 ℃), soluble in ethanol, slightly soluble in ether
-pKa value: pKa = 2.98,pKa = 4.34, binary acidic

2. D(-)-tartaric acid (synthetic)
-Absolute configuration:(2S,3S)
-Optical activity: levorotatory, specific rotation [α] D²⁰= -12.0 ° to -12.8 °
-Physical properties: basically the same as L( )-tartaric acid, only the opposite direction of optical rotation
-Source: mainly obtained by chemical resolution or biological transformation, very little natural

3. DL-tartaric acid (racemate)
-Composition: equal mixture of L (-)-tartaric acid and D(-)-tartaric acid
-Optical activity: no optical rotation (internal and external optical rotation cancel each other)
-Physical properties: melting point 206 ℃, significantly higher than the single enantiomer
-Solubility: 20.6g/100 mL water, much lower than L-type

4. meso-tartaric acid (mesoform)
-Absolute configuration:(2R,3S) or (2S,3R)
-Optical activity: no optical rotation (there is a symmetry plane inside the molecule)
-Physical properties: melting point 146-150 ℃, is the lowest melting point of the four isomers
-pKa value: pKa = 3.22,pKa = 4.86, acidity weaker than L-type

The key differences between the four isomers are not only reflected in the physical properties, but more importantly, there are significant differences in their biological activities. Due to the chiral selectivity of the enzyme system in organisms, L (+)-tartaric acid can be metabolized normally, while the bioavailability and metabolic pathways of D-type and meso-type are different, which is also an important reason why only L (+)-tartaric acid is allowed to be used in the field of food additives.

Chemical structure and properties of 2.
The molecular structure of L (+)-tartaric acid has four dissociable hydroxyl groups and two carboxyl groups. This multifunctional structure gives it a variety of chemical reactivity:

1. Acidic dissociation: As a dicarboxylic acid, L( )-tartaric acid can be dissociated step by step to produce H ions, which is more acidic than other edible organic acids such as citric acid and malic acid, and is especially suitable for food systems that require rapid acidification.

2. Chelation: The hydroxyl and carboxyl groups in the molecule can form stable five-or six-element chelates with various metal ions such as Fe, Cu, Ca, etc. This feature enables it to have the functions of antioxidant efficiency, browning prevention, color stability and the like in food.

3. Salt forming reaction: it can form a variety of salts with sodium, potassium, calcium, ammonium and other cations, including potassium hydrogen tartrate, sodium tartrate, potassium sodium tartrate (Rochelle salt), etc. These derivatives have unique application value.

4. Esterification reaction: It can be esterified with alcohols to generate tartaric acid ester compounds, such as diethyl tartrate, dibutyl tartrate, etc., which are used as chiral resolution reagents and plasticizers.

3. identification method
1. Optical rotation method: L( )-tartaric acid can be directly distinguished from other isomers by determining the specific rotation
2. Chemical identification: add silver nitrate solution to generate white precipitate, add ammonia solution and heat after separation to generate silver mirror reaction
3. Resorcinol test: in sulfuric acid medium and resorcinol co-heating, dark blue, red after dilution
4. Infrared spectroscopy: the characteristic absorption peak should be consistent with the standard map

L(+)-tartaric acid industry is an important market segment in the field of food additives, and it also spans many industrial fields such as fine chemicals and pharmaceutical intermediates. After decades of development, the world has formed a dual supply pattern based on European natural extraction and Asian chemical synthesis.

1. global industrial pattern
1. Regional distribution characteristics
Europe is the traditional production base of L(+)-tartaric acid, mainly relying on its developed wine industry, through the recovery of tartaric acid (potassium hydrogen tartrate precipitated in the winemaking process) for production. The production capacity of L(+)-tartaric acid in major wine producing countries such as France, Italy and Spain accounts for more than 70% of the global production capacity from natural sources. An Italian company is the world's largest producer of natural tartaric acid, with an annual capacity of more than 50000 tons of tartar.

Asia, especially China, has become a major producer of L(+)-tartaric acid by chemical synthesis. With the advantage of raw material cost and the continuous improvement of technical level, the share of Chinese enterprises in the international market continues to expand. As of 2024, China's total production capacity of L(+)-tartaric acid is about 48000 tons/year, the actual output is 39000 tons, and the capacity utilization rate is 81.3, accounting for more than 60% of the global total output.

2. Market size and growth
According to the Grand View Research 2024 report, the global tartaric acid market will reach $3.5 billion in 2023 and is expected to grow to $5 billion in 2028, with a compound annual growth rate (CAGR) of 7.2 percent. Among them, L (plus)-tartaric acid due to natural properties and regulatory advantages, the growth rate is higher than the overall market, CAGR is expected to reach 8.5.

China's L (plus)-tartaric acid market is about RMB 1.5 billion in 2023, with a compound growth rate of 7.2 in 2020-2023. It is expected to maintain an average annual growth rate of 6-8% from 2025 to 2030, and the market size is expected to reach 22-2.5 billion yuan by 2030.

2. China Industry Status Quo
1. Capacity layout and concentration
China's L(+)-tartaric acid industry is highly concentrated, with the top five production enterprises accounting for more than 78% of the total production capacity. In terms of regional distribution, Jiangsu, Shandong and Zhejiang provinces constitute the core production areas, with the total production capacity accounting for more than 85% of the national total.

Jiangsu Province is the region with the most intensive production capacity. The annual production capacity of a chemical enterprise exceeds 12000 tons, ranking first in China for many years. The optical purity of its products is stable at more than 99.5, which is widely used in the field of food additives and chiral drug synthesis. Relying on the advantages of basic chemical raw materials, Shandong Province has formed an industrial cluster represented by Luwei Pharmaceutical, with a total annual production capacity of about 13000 tons.

2. Production process route
The production of L(+)-tartaric acid in China is mainly based on chemical synthesis, supplemented by natural extraction. The maleic anhydride (MA) oxidation-hydrolysis-resolution process accounts for 92% of the total production capacity, while the natural L(+)-tartaric acid extracted from wine by-products has a production capacity of only about 4,000 tons/year, accounting for less than 8%.

This structural difference stems from: first, the relatively small scale of China's wine industry, the limited resources of the stone; second, the cost advantage of the chemical synthesis method is obvious, the raw material MA can be obtained from the petrochemical route on a large scale; third, the maturity of the chiral separation technology enables the synthesis method to obtain high optical purity products stably.

3. downstream application structure
Downstream applications of L(+)-tartaric acid are diversified, but the food and beverage industry dominates:

1. Food and beverage industry: accounting for 58.7 per cent, including wine brewing (adjusting acidity and stabilizing color), baked goods (leavening agent components), beverages (acidifiers, especially suitable for grape-flavored drinks), candy (preventing sucrose crystallization), etc.

2. Pharmaceutical industry: accounting for 24.3, mainly used for chiral drug synthesis (such as levodopa, metoprolol tartrate), drug salt forming agent, pH regulator, slow-controlled release preparation excipients, etc.

3. Chemical and other industries: 17.0 per cent, including electroplating complexing agents, cement retarders, leather tanning agents, printing and dyeing mordants, electronic component cleaners, etc.

4. import and export trade
In 2024, China's total exports of L(+)-tartaric acid and its salts reached 12,850 tons, up 9.6 percent year-on-year, and the export value was about US $48.7 million billion, up 11.2 percent year-on-year. Export destinations are highly concentrated:
-EU: 32.5 per cent, supported by rigid demand in the food and beverage and pharmaceutical industries
-US: 21.7 percent, natural food additive regulations tightened to boost demand
-India: 18.4 percent (fastest growth), led by pharmaceutical expansion
-Japan and South Korea: about 16% combined

In the export product structure, food grade L(+)-tartaric acid accounts for 65%, industrial grade accounts for 28%, and pharmaceutical grade accounts for 7%. Although the proportion of pharmaceutical grade products is not high, the export growth rate will reach 32% in 2024, which shows that the competitiveness of Chinese enterprises in the high-end market is improving.

In terms of imports, China imports about 300-500 tons of special specification L(+)-tartaric acid each year, mainly ultra-high purity (≥ 99.9%) electronic grade and specific pharmacopoeia grade products, mainly from Germany, Italy and the United States.

Challenges facing the 5. industry
1. dependence on raw materials: chemical synthesis is highly dependent on MA (maleic anhydride), and MA prices are greatly affected by oil price fluctuations, high international oil prices in 2022 had led to a decline in the industry's gross profit margin of about 8 percentage points.
2. Environmental pressure: the traditional oxidation process of chromium-containing wastewater treatment costs are high, environmental regulations tighten to increase the operating costs of enterprises.
3. High-end market breakthrough: pharmaceutical and electronic products still have technical bottlenecks, import dependence is high.
4. Insufficient natural production capacity: In the face of rising global demand for natural food additives, China's natural tartaric acid production capacity is limited.

As an important food additive and chemical raw material, L(+)-tartaric acid is strictly regulated by many international and domestic standard systems. These standards cover physical and chemical indicators, testing methods, scope of use and other dimensions to ensure product quality and safety and application compliance.

1. international standard system

1. JECFA evaluation and ADI value
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) conducted a comprehensive evaluation of L(+)-tartaric acid at its 53rd meeting and established an acceptable daily intake (ADI) value.

-ADI value: 0-30 mg/kg bw (as tartaric acid)
-Evaluation conclusion: L(+)-tartaric acid has no carcinogenicity, mutagenicity and reproductive toxicity within the recommended range of use, and has good safety.
-Metabolic data: more than 99% of the human body is excreted by urine within 24 hours after oral administration, without accumulation in the body
-Special note: D(-)-tartaric acid and meso-tartaric acid have different metabolic pathways and are not approved as food additives by JECFA

JECFA has also developed detailed specifications for L(+)-tartaric acid, including:
-Content (dry basis):≥ 99.5%
-specific rotation: +11.5 ° to +13.5 °
-Sulphate (in SOH):≤ 0.05 per cent
-Oxalate: ≤ 0.035%
-Heavy metals (as Pb):≤ 10 mg/kg
-Arsenic (As):≤ 2 mg/kg

2. FCC Food Chemicals Code
The Food Chemicals Codex (FCC) is an internationally recognized quality standard for food additives. The current version is FCC 12 (issued in 2024).

Key technical requirements of FCC for L(+)-tartaric acid:
-Identification test: need to be determined by infrared spectral comparison and specific rotation
-Content determination: C? H? O? (anhydrous basis) 99.7-100.5
-Specific optical rotation [α] D²↓: +12.0 ° to +12.8 °(20% aqueous solution)
-Loss on drying: ≤ 0.5%(105 ℃,3 hours)
-Residue on ignition: ≤ 0.05%
-Heavy metals: ≤ 5 mg/kg
-Lead: ≤ 2 mg/kg(ICP-MS method)
-Selenium: ≤ 5 mg/kg
-easy oxide: through the test

FCC standards are more stringent than JECFA, especially in terms of heavy metal limits, which is also the threshold that must be met for export to the US market. FCC certification has become a pass for food additives to enter the North American market.

3. EU regulatory standards
The European Food Safety Authority (EFSA) has assessed L(+)-tartaric acid in accordance with JECFA and approved it for use as a food additive, number E 334.

-Use principle: according to GMP (good manufacturing practice) appropriate use
-Special regulations: not for infant food (except for specific nutritional purposes)
-Label requirements: "Tartaric acid (L(+)-)" or "E 334"
-Purity standard: basically consistent with FCC, specific rotation requirements +11.5 ° to +13.5 °

4. Pharmacopoeia standards
The application of L(+)-tartaric acid in the field of medicine must meet the requirements of national pharmacopoeia:

-Chinese Pharmacopoeia (ChP 2025): specific rotation +12.0 ° to +12.8 °, content ≥ 99.5%
-European Pharmacopoeia (EP 11.0): specific rotation +11.5 ° to +13.5 °, including bacterial endotoxin test
-United States Pharmacopeia (USP-NF 2024): Tighter control of impurities than optical rotation +12.05 ° to +12.85 °

2. China National Standard System

1. GB 25545-2010 National Food Safety Standard Food Additive L(+)-Tartaric Acid
This is a mandatory national standard for L(+)-tartaric acid food-grade products in China, issued and implemented by the National Health Commission.

Core technical indicators:
-Sensory requirements: colorless crystal or white crystalline powder, no peculiar smell
-L(+)-tartaric acid content (C? H? O?, dry basis):≥ 99.5
-specific rotation [α]D²: +12.0 ° to +12.8 °
-Loss on drying: ≤ 0.5%(105 ℃,3h)
-Residue on ignition: ≤ 0.1%
-Sulphate (in SOH):≤ 0.04 per cent
-Oxalate (in C₂ OHg):≤ 0.035%
-easy oxide: through the test
-Heavy metals (as Pb):≤ 10 mg/kg
-Lead (Pb):≤ 2 mg/kg(GB 5009.12 method)
-Arsenic (As):≤ 2 mg/kg

The detection method system includes:
-Content determination: sodium hydroxide standard solution titration, phenolphthalein indicator
-Specific rotation: as per GB/T 613
-Heavy metals: colorimetric method, hydrogen sulfide test solution
-Lead/Arsenic: Atomic Absorption Spectrometry or Inductively Coupled Plasma Mass Spectrometry

2. GB 1886.42-2015 "national food safety standard food additive dl-tartaric acid"
This standard is applicable to racemic tartaric acid prepared by oxidation and hydrolysis with maleic anhydride and hydrogen peroxide as raw materials. The main differences between the standard and L(+)-tartaric acid are as follows:
-Optical rotation: no optical rotation requirements (racemic body)
-Melting point: 200-206 ℃ (significantly higher than 168-172 ℃ of L-type)
-Scope of use: subject to more stringent restrictions, some food categories are not allowed to use

3. GB 2760-2024 Standard for the Use of Food Additives
The standard specifies the scope and maximum use of L(+)-tartaric acid as an acidity regulator (functional category 01.111):

| Food Classification Number | Food Name | Maximum Usage (g/kg) | Remarks |
| ------------ | ---------- | --------------- | ---------- |
| 04.02.02.03 | Pickled Vegetables | 3.0 | Based on Tartaric Acid |
| 05.02 | Candy | Use appropriate amount according to production needs | - |
| 05.02.01 | Gum base candy | Use appropriate amount according to production needs | - |
| 05.02.02 | Candy other than gum base candy | Use appropriate amount according to production needs | - |
| 06.03.02.05 | Fried flour products | 10.0 | As tartaric acid |
| 06.05.02.01 | vermicelli, vermicelli | 2.0 | in terms of tartaric acid |
| 06.11 | batter, wrapping powder, frying powder | 10.0 | as tartaric acid |
| 12.10.01 | Solid compound seasoning | 10.0 | As tartaric acid |
| 14.02.03 | Fruit and vegetable juice (pulp) beverages | 5.0 | in terms of tartaric acid |
| 14.03.02 | Vegetable Protein Drink | 5.0 | As Tartaric Acid |
| 14.03.03 | Compound protein beverage | 5.0 | As tartaric acid |
| 14.04 | Carbonated Drinks | 5.0 | As Tartaric Acid |
| 14.05 | Tea, Coffee, Vegetable Beverage | 5.0 | As Tartaric Acid |
| 14.07 | Special Purpose Beverages | 5.0 | As Tartaric Acid |

4. GB/T 15358-2020 Tartaric Acid for Industrial Use
The industrial grade L(+)-tartaric acid product standard divides the products into three grades: superior products, first-class products and qualified products, with the main differences in content and heavy metal indicators.

Development Trend of 3. Standards
1. Tighter indicators: heavy metal limits continue to tighten, especially lead, arsenic and other toxic elements, FCC 12 has reduced the lead limit from 10 mg/kg to 2 mg/kg
2. Method update: the detection technology is continuously upgraded, from traditional chemical method to instrument analysis, such as HPLC chiral column direct determination of enantiomeric purity
3. New standards: special standards for high-end products such as pharmaceutical grade and electronic grade are being formulated.
4. International coordination: the differences between national standards are gradually narrowing and the degree of mutual recognition is improved, which is conducive to the development of international trade.