We prove that every proper polynomial of degree at least 869316301880&_mathId=si1.gif&_user=111111111&_pii=S0021869316301880&_rdoc=1&_issn=00218693&md5=eea8e0af3be6507c6a743dab1005d87e" title="Click to view the MathML source">2n−2 is an identity of commutative alternative algebra of rank 869316301880&_mathId=si2.gif&_user=111111111&_pii=S0021869316301880&_rdoc=1&_issn=00218693&md5=b89774e999cb86661ee795136b29fc35" title="Click to view the MathML source">n⩾3. Using this we deduce that every commutative alternative algebra of rank n with the identity 869316301880&_mathId=si3.gif&_user=111111111&_pii=S0021869316301880&_rdoc=1&_issn=00218693&md5=a98cd3589e1e3a26ce836c50ad409806" title="Click to view the MathML source">x3=0 is nilpotent of index at most 869316301880&_mathId=si23.gif&_user=111111111&_pii=S0021869316301880&_rdoc=1&_issn=00218693&md5=adbcfde9d0baa892ebc335ec88f4c249" title="Click to view the MathML source">4n−2. We also prove that the index of nilpotency of the associator ideal in the free commutative alternative algebra of rank 869316301880&_mathId=si2.gif&_user=111111111&_pii=S0021869316301880&_rdoc=1&_issn=00218693&md5=b89774e999cb86661ee795136b29fc35" title="Click to view the MathML source">n⩾3 is equal to 869316301880&_mathId=si312.gif&_user=111111111&_pii=S0021869316301880&_rdoc=1&_issn=00218693&md5=ec232d9fb24caacdc5d8f9e358544c8b">869316301880-si312.gif">.