The two 6% contaminants in 4-Chloro-1,8-naphthalic anhydride (94%) are likely related derivatives or byproducts of the compound's synthesis and purification process. Based on the available research, the common contaminants typically include:

These impurities are likely visible on TLC as distinct spots under UV light due to their structural similarities and retained aromatic properties.

In summary, the two contaminants are most likely 3-hydroxy-4-chloro-1,8-naphthalic anhydride and 5,8-dichloro-1-naphthoic acid, which are byproducts of the chemical synthesis and purification processes for 4-chloro-1,8-naphthalic anhydride.

• Chen, J., Smith, V., & Huffman, J. (2010). 8-Chloro- and 5,8-Dichloro-1-naphthoic acids. Organic Preparations and Procedures International, 42(4), 490-493.
• Haiyun, Z. (2009). Molecular design and solvent-free synthesis of 3-hydroxy-4-chloro-1,8-naphthalic anhydride under microwave irradiation conditions. Chemical Research and Application.